| Message ID | 1463664426-2991-1-git-send-email-wanpeng.li@hotmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 05/19/2016 03:27 PM, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > If an emulated lapic timer will fire soon(in the scope of 10us the > base of dynamic halt-polling, lower-end of message passing workload > latency TCP_RR's poll time < 10us) we can treat it as a short halt, > and poll to wait it fire, the fire callback apic_timer_fn() will set > KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. > This can avoid context switch overhead and the latency which we wake > up vCPU. > > iperf TCP get ~6% bandwidth improvement. > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: David Matlack <dmatlack@google.com> > Cc: Christian Borntraeger <borntraeger@de.ibm.com> > Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> Looks good to me. I have not checked what happens when I provide an s390 implementation so I cannot say anything about performance. It looks like it does not hurt on s390 - which is what I would expect. > --- > v1 -> v2: > * add return statement to non-x86 archs > * capture never expire case for x86 (hrtimer is not started) > > arch/arm/include/asm/kvm_host.h | 4 ++++ > arch/arm64/include/asm/kvm_host.h | 4 ++++ > arch/mips/include/asm/kvm_host.h | 4 ++++ > arch/powerpc/include/asm/kvm_host.h | 4 ++++ > arch/s390/include/asm/kvm_host.h | 4 ++++ > arch/x86/kvm/lapic.c | 11 +++++++++++ > arch/x86/kvm/lapic.h | 1 + > arch/x86/kvm/x86.c | 5 +++++ > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 14 ++++++++++---- > 10 files changed, 48 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h > index 4cd8732..a5fd858 100644 > --- a/arch/arm/include/asm/kvm_host.h > +++ b/arch/arm/include/asm/kvm_host.h > @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} > static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > static inline void kvm_arm_init_debug(void) {} > static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index d49399d..94e227a 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} > static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > void kvm_arm_init_debug(void); > void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); > diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h > index 9a37a10..456bc42 100644 > --- a/arch/mips/include/asm/kvm_host.h > +++ b/arch/mips/include/asm/kvm_host.h > @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > > #endif /* __MIPS_KVM_HOST_H__ */ > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index ec35af3..5986c79 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > #endif /* __POWERPC_KVM_HOST_H__ */ > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h > index 37b9017..bdb01a1 100644 > --- a/arch/s390/include/asm/kvm_host.h > +++ b/arch/s390/include/asm/kvm_host.h > @@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm, > struct kvm_memory_slot *slot) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index bbb5b28..cfeeac3 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic) > return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE; > } > > +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) > +{ > + struct kvm_lapic *apic = vcpu->arch.apic; > + struct hrtimer *timer = &apic->lapic_timer.timer; > + > + if (!hrtimer_active(timer)) > + return -1ULL; > + else > + return ktime_to_ns(hrtimer_get_remaining(timer)); > +} > + > static inline int apic_lvt_nmi_mode(u32 lvt_val) > { > return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI; > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index 891c6da..ee4da6c 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, > struct kvm_vcpu **dest_vcpu); > int kvm_vector_to_index(u32 vector, u32 dest_vcpus, > const unsigned long *bitmap, u32 bitmap_size); > +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); > #endif > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index a8c7ca3..9b5ad99 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) > struct static_key kvm_no_apic_vcpu __read_mostly; > EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); > > +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return apic_get_timer_expire(vcpu); > +} > + > int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) > { > struct page *page; > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index b1fa8f1..14d6c23 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); > void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); > void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); > void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); > +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); > > void kvm_flush_remote_tlbs(struct kvm *kvm); > void kvm_reload_remote_mmus(struct kvm *kvm); > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index dd4ac9d..e4bb30b 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR); > static unsigned int halt_poll_ns_shrink; > module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); > > +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */ > +static unsigned int halt_poll_ns_base = 10000; > + > /* > * Ordering of locks: > * > @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) > grow = READ_ONCE(halt_poll_ns_grow); > /* 10us base */ > if (val == 0 && grow) > - val = 10000; > + val = halt_poll_ns_base; > else > val *= grow; > > @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) > ktime_t start, cur; > DECLARE_SWAITQUEUE(wait); > bool waited = false; > - u64 block_ns; > + u64 block_ns, delta, remaining; > > + remaining = kvm_arch_timer_remaining(vcpu); > start = cur = ktime_get(); > - if (vcpu->halt_poll_ns) { > - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); > + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { > + ktime_t stop; > > + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining; > + stop = ktime_add_ns(ktime_get(), delta); > ++vcpu->stat.halt_attempted_poll; > do { > /* > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > If an emulated lapic timer will fire soon(in the scope of 10us the > base of dynamic halt-polling, lower-end of message passing workload > latency TCP_RR's poll time < 10us) we can treat it as a short halt, > and poll to wait it fire, the fire callback apic_timer_fn() will set > KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. > This can avoid context switch overhead and the latency which we wake > up vCPU. If I understand correctly, your patch aims to reduce the latency of (APIC Timer expires) -> (Guest resumes execution) using halt-polling. Let me know if I'm misunderstanding. In general, I don't think it makes sense to poll for timer interrupts. We know when the timer interrupt is going to arrive. If we care about the latency of delivering that interrupt to the guest, we should program the hrtimer to wake us up slightly early, and then deliver the virtual timer interrupt right on time (I think KVM's TSC Deadline Timer emulation already does this). I'm curious to know if this scheme would give the same performance improvement to iperf as your patch. We discussed this a bit before on the mailing list before (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling and timer interrupts go in the opposite direction: if the next timer event (from any timer) is less than vcpu->halt_poll_ns, don't poll at all. > > iperf TCP get ~6% bandwidth improvement. Can you explain why your patch results in this bandwidth improvement? > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: David Matlack <dmatlack@google.com> > Cc: Christian Borntraeger <borntraeger@de.ibm.com> > Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> > --- > v1 -> v2: > * add return statement to non-x86 archs > * capture never expire case for x86 (hrtimer is not started) > > arch/arm/include/asm/kvm_host.h | 4 ++++ > arch/arm64/include/asm/kvm_host.h | 4 ++++ > arch/mips/include/asm/kvm_host.h | 4 ++++ > arch/powerpc/include/asm/kvm_host.h | 4 ++++ > arch/s390/include/asm/kvm_host.h | 4 ++++ > arch/x86/kvm/lapic.c | 11 +++++++++++ > arch/x86/kvm/lapic.h | 1 + > arch/x86/kvm/x86.c | 5 +++++ > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 14 ++++++++++---- > 10 files changed, 48 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h > index 4cd8732..a5fd858 100644 > --- a/arch/arm/include/asm/kvm_host.h > +++ b/arch/arm/include/asm/kvm_host.h > @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} > static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > static inline void kvm_arm_init_debug(void) {} > static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index d49399d..94e227a 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} > static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > void kvm_arm_init_debug(void); > void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); > diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h > index 9a37a10..456bc42 100644 > --- a/arch/mips/include/asm/kvm_host.h > +++ b/arch/mips/include/asm/kvm_host.h > @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > > #endif /* __MIPS_KVM_HOST_H__ */ > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index ec35af3..5986c79 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > #endif /* __POWERPC_KVM_HOST_H__ */ > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h > index 37b9017..bdb01a1 100644 > --- a/arch/s390/include/asm/kvm_host.h > +++ b/arch/s390/include/asm/kvm_host.h > @@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm, > struct kvm_memory_slot *slot) {} > static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} > static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} > +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return -1ULL; > +} > > void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index bbb5b28..cfeeac3 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic) > return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE; > } > > +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) > +{ > + struct kvm_lapic *apic = vcpu->arch.apic; > + struct hrtimer *timer = &apic->lapic_timer.timer; > + > + if (!hrtimer_active(timer)) > + return -1ULL; > + else > + return ktime_to_ns(hrtimer_get_remaining(timer)); > +} > + > static inline int apic_lvt_nmi_mode(u32 lvt_val) > { > return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI; > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index 891c6da..ee4da6c 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, > struct kvm_vcpu **dest_vcpu); > int kvm_vector_to_index(u32 vector, u32 dest_vcpus, > const unsigned long *bitmap, u32 bitmap_size); > +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); > #endif > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index a8c7ca3..9b5ad99 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) > struct static_key kvm_no_apic_vcpu __read_mostly; > EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); > > +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) > +{ > + return apic_get_timer_expire(vcpu); > +} > + > int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) > { > struct page *page; > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index b1fa8f1..14d6c23 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); > void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); > void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); > void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); > +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); > > void kvm_flush_remote_tlbs(struct kvm *kvm); > void kvm_reload_remote_mmus(struct kvm *kvm); > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index dd4ac9d..e4bb30b 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR); > static unsigned int halt_poll_ns_shrink; > module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); > > +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */ > +static unsigned int halt_poll_ns_base = 10000; > + > /* > * Ordering of locks: > * > @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) > grow = READ_ONCE(halt_poll_ns_grow); > /* 10us base */ > if (val == 0 && grow) > - val = 10000; > + val = halt_poll_ns_base; > else > val *= grow; > > @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) > ktime_t start, cur; > DECLARE_SWAITQUEUE(wait); > bool waited = false; > - u64 block_ns; > + u64 block_ns, delta, remaining; > > + remaining = kvm_arch_timer_remaining(vcpu); > start = cur = ktime_get(); > - if (vcpu->halt_poll_ns) { > - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); > + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { > + ktime_t stop; > > + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining; > + stop = ktime_add_ns(ktime_get(), delta); > ++vcpu->stat.halt_attempted_poll; > do { > /* > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, May 19, 2016 at 11:01 AM, David Matlack <dmatlack@google.com> wrote: > On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >> From: Wanpeng Li <wanpeng.li@hotmail.com> >> >> If an emulated lapic timer will fire soon(in the scope of 10us the >> base of dynamic halt-polling, lower-end of message passing workload >> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >> and poll to wait it fire, the fire callback apic_timer_fn() will set >> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >> This can avoid context switch overhead and the latency which we wake >> up vCPU. > > If I understand correctly, your patch aims to reduce the latency of > (APIC Timer expires) -> (Guest resumes execution) using halt-polling. > Let me know if I'm misunderstanding. > > In general, I don't think it makes sense to poll for timer interrupts. > We know when the timer interrupt is going to arrive. If we care about > the latency of delivering that interrupt to the guest, we should > program the hrtimer to wake us up slightly early, and then deliver the > virtual timer interrupt right on time (I think KVM's TSC Deadline > Timer emulation already does this). (It looks like the way to enable this feature is to set the module parameter lapic_timer_advance_ns and make sure your guest is using the TSC Deadline timer instead of the APIC Timer.) > I'm curious to know if this scheme > would give the same performance improvement to iperf as your patch. > > We discussed this a bit before on the mailing list before > (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling > and timer interrupts go in the opposite direction: if the next timer > event (from any timer) is less than vcpu->halt_poll_ns, don't poll at > all. > >> >> iperf TCP get ~6% bandwidth improvement. > > Can you explain why your patch results in this bandwidth improvement? > >> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Radim Krčmář <rkrcmar@redhat.com> >> Cc: David Matlack <dmatlack@google.com> >> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >> --- >> v1 -> v2: >> * add return statement to non-x86 archs >> * capture never expire case for x86 (hrtimer is not started) >> >> arch/arm/include/asm/kvm_host.h | 4 ++++ >> arch/arm64/include/asm/kvm_host.h | 4 ++++ >> arch/mips/include/asm/kvm_host.h | 4 ++++ >> arch/powerpc/include/asm/kvm_host.h | 4 ++++ >> arch/s390/include/asm/kvm_host.h | 4 ++++ >> arch/x86/kvm/lapic.c | 11 +++++++++++ >> arch/x86/kvm/lapic.h | 1 + >> arch/x86/kvm/x86.c | 5 +++++ >> include/linux/kvm_host.h | 1 + >> virt/kvm/kvm_main.c | 14 ++++++++++---- >> 10 files changed, 48 insertions(+), 4 deletions(-) >> >> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h >> index 4cd8732..a5fd858 100644 >> --- a/arch/arm/include/asm/kvm_host.h >> +++ b/arch/arm/include/asm/kvm_host.h >> @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} >> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return -1ULL; >> +} >> >> static inline void kvm_arm_init_debug(void) {} >> static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} >> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >> index d49399d..94e227a 100644 >> --- a/arch/arm64/include/asm/kvm_host.h >> +++ b/arch/arm64/include/asm/kvm_host.h >> @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} >> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return -1ULL; >> +} >> >> void kvm_arm_init_debug(void); >> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); >> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h >> index 9a37a10..456bc42 100644 >> --- a/arch/mips/include/asm/kvm_host.h >> +++ b/arch/mips/include/asm/kvm_host.h >> @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return -1ULL; >> +} >> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >> >> #endif /* __MIPS_KVM_HOST_H__ */ >> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h >> index ec35af3..5986c79 100644 >> --- a/arch/powerpc/include/asm/kvm_host.h >> +++ b/arch/powerpc/include/asm/kvm_host.h >> @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} >> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return -1ULL; >> +} >> >> #endif /* __POWERPC_KVM_HOST_H__ */ >> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h >> index 37b9017..bdb01a1 100644 >> --- a/arch/s390/include/asm/kvm_host.h >> +++ b/arch/s390/include/asm/kvm_host.h >> @@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm, >> struct kvm_memory_slot *slot) {} >> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return -1ULL; >> +} >> >> void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); >> >> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >> index bbb5b28..cfeeac3 100644 >> --- a/arch/x86/kvm/lapic.c >> +++ b/arch/x86/kvm/lapic.c >> @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic) >> return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE; >> } >> >> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) >> +{ >> + struct kvm_lapic *apic = vcpu->arch.apic; >> + struct hrtimer *timer = &apic->lapic_timer.timer; >> + >> + if (!hrtimer_active(timer)) >> + return -1ULL; >> + else >> + return ktime_to_ns(hrtimer_get_remaining(timer)); >> +} >> + >> static inline int apic_lvt_nmi_mode(u32 lvt_val) >> { >> return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI; >> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h >> index 891c6da..ee4da6c 100644 >> --- a/arch/x86/kvm/lapic.h >> +++ b/arch/x86/kvm/lapic.h >> @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, >> struct kvm_vcpu **dest_vcpu); >> int kvm_vector_to_index(u32 vector, u32 dest_vcpus, >> const unsigned long *bitmap, u32 bitmap_size); >> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); >> #endif >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index a8c7ca3..9b5ad99 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) >> struct static_key kvm_no_apic_vcpu __read_mostly; >> EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); >> >> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >> +{ >> + return apic_get_timer_expire(vcpu); >> +} >> + >> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) >> { >> struct page *page; >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> index b1fa8f1..14d6c23 100644 >> --- a/include/linux/kvm_host.h >> +++ b/include/linux/kvm_host.h >> @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); >> void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); >> void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); >> void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); >> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); >> >> void kvm_flush_remote_tlbs(struct kvm *kvm); >> void kvm_reload_remote_mmus(struct kvm *kvm); >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index dd4ac9d..e4bb30b 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR); >> static unsigned int halt_poll_ns_shrink; >> module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); >> >> +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */ >> +static unsigned int halt_poll_ns_base = 10000; >> + >> /* >> * Ordering of locks: >> * >> @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) >> grow = READ_ONCE(halt_poll_ns_grow); >> /* 10us base */ >> if (val == 0 && grow) >> - val = 10000; >> + val = halt_poll_ns_base; >> else >> val *= grow; >> >> @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) >> ktime_t start, cur; >> DECLARE_SWAITQUEUE(wait); >> bool waited = false; >> - u64 block_ns; >> + u64 block_ns, delta, remaining; >> >> + remaining = kvm_arch_timer_remaining(vcpu); >> start = cur = ktime_get(); >> - if (vcpu->halt_poll_ns) { >> - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); >> + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { >> + ktime_t stop; >> >> + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining; >> + stop = ktime_add_ns(ktime_get(), delta); >> ++vcpu->stat.halt_attempted_poll; >> do { >> /* >> -- >> 1.9.1 >> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2016/5/20 2:36, David Matlack wrote: > On Thu, May 19, 2016 at 11:01 AM, David Matlack <dmatlack@google.com> wrote: >> On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>> >>> If an emulated lapic timer will fire soon(in the scope of 10us the >>> base of dynamic halt-polling, lower-end of message passing workload >>> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >>> and poll to wait it fire, the fire callback apic_timer_fn() will set >>> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >>> This can avoid context switch overhead and the latency which we wake >>> up vCPU. >> >> If I understand correctly, your patch aims to reduce the latency of >> (APIC Timer expires) -> (Guest resumes execution) using halt-polling. >> Let me know if I'm misunderstanding. >> >> In general, I don't think it makes sense to poll for timer interrupts. >> We know when the timer interrupt is going to arrive. If we care about >> the latency of delivering that interrupt to the guest, we should >> program the hrtimer to wake us up slightly early, and then deliver the >> virtual timer interrupt right on time (I think KVM's TSC Deadline >> Timer emulation already does this). > > (It looks like the way to enable this feature is to set the module > parameter lapic_timer_advance_ns and make sure your guest is using the > TSC Deadline timer instead of the APIC Timer.) This feature is slightly different from current advance expiration way. Advance expiration rely on the VCPU is running(do polling before vmentry). But in some cases, the timer interrupt may be blocked by other thread(i.e., IF bit is clear) and VCPU cannot be scheduled to run immediately. So even advance the timer early, VCPU may still see the latency. But polling is different, it ensures the VCPU to aware the timer expiration before schedule out. > >> I'm curious to know if this scheme >> would give the same performance improvement to iperf as your patch. >> >> We discussed this a bit before on the mailing list before >> (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling >> and timer interrupts go in the opposite direction: if the next timer >> event (from any timer) is less than vcpu->halt_poll_ns, don't poll at >> all. >> >>> >>> iperf TCP get ~6% bandwidth improvement. >> >> Can you explain why your patch results in this bandwidth improvement? It should be reasonable. I have seen the same improvement with ctx switch benchmark: The latency is reduce from ~2600ns to ~2300ns with the similar mechanism.(The same idea but different implementation) >> >>> >>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>> Cc: David Matlack <dmatlack@google.com> >>> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>> --- >>> v1 -> v2: >>> * add return statement to non-x86 archs >>> * capture never expire case for x86 (hrtimer is not started) >>> >>> arch/arm/include/asm/kvm_host.h | 4 ++++ >>> arch/arm64/include/asm/kvm_host.h | 4 ++++ >>> arch/mips/include/asm/kvm_host.h | 4 ++++ >>> arch/powerpc/include/asm/kvm_host.h | 4 ++++ >>> arch/s390/include/asm/kvm_host.h | 4 ++++ >>> arch/x86/kvm/lapic.c | 11 +++++++++++ >>> arch/x86/kvm/lapic.h | 1 + >>> arch/x86/kvm/x86.c | 5 +++++ >>> include/linux/kvm_host.h | 1 + >>> virt/kvm/kvm_main.c | 14 ++++++++++---- >>> 10 files changed, 48 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h >>> index 4cd8732..a5fd858 100644 >>> --- a/arch/arm/include/asm/kvm_host.h >>> +++ b/arch/arm/include/asm/kvm_host.h >>> @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} >>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return -1ULL; >>> +} >>> >>> static inline void kvm_arm_init_debug(void) {} >>> static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} >>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >>> index d49399d..94e227a 100644 >>> --- a/arch/arm64/include/asm/kvm_host.h >>> +++ b/arch/arm64/include/asm/kvm_host.h >>> @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} >>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return -1ULL; >>> +} >>> >>> void kvm_arm_init_debug(void); >>> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); >>> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h >>> index 9a37a10..456bc42 100644 >>> --- a/arch/mips/include/asm/kvm_host.h >>> +++ b/arch/mips/include/asm/kvm_host.h >>> @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return -1ULL; >>> +} >>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>> >>> #endif /* __MIPS_KVM_HOST_H__ */ >>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h >>> index ec35af3..5986c79 100644 >>> --- a/arch/powerpc/include/asm/kvm_host.h >>> +++ b/arch/powerpc/include/asm/kvm_host.h >>> @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} >>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return -1ULL; >>> +} >>> >>> #endif /* __POWERPC_KVM_HOST_H__ */ >>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h >>> index 37b9017..bdb01a1 100644 >>> --- a/arch/s390/include/asm/kvm_host.h >>> +++ b/arch/s390/include/asm/kvm_host.h >>> @@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm, >>> struct kvm_memory_slot *slot) {} >>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return -1ULL; >>> +} >>> >>> void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); >>> >>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >>> index bbb5b28..cfeeac3 100644 >>> --- a/arch/x86/kvm/lapic.c >>> +++ b/arch/x86/kvm/lapic.c >>> @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic) >>> return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE; >>> } >>> >>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) >>> +{ >>> + struct kvm_lapic *apic = vcpu->arch.apic; >>> + struct hrtimer *timer = &apic->lapic_timer.timer; >>> + >>> + if (!hrtimer_active(timer)) >>> + return -1ULL; >>> + else >>> + return ktime_to_ns(hrtimer_get_remaining(timer)); >>> +} >>> + >>> static inline int apic_lvt_nmi_mode(u32 lvt_val) >>> { >>> return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI; >>> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h >>> index 891c6da..ee4da6c 100644 >>> --- a/arch/x86/kvm/lapic.h >>> +++ b/arch/x86/kvm/lapic.h >>> @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, >>> struct kvm_vcpu **dest_vcpu); >>> int kvm_vector_to_index(u32 vector, u32 dest_vcpus, >>> const unsigned long *bitmap, u32 bitmap_size); >>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); >>> #endif >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index a8c7ca3..9b5ad99 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) >>> struct static_key kvm_no_apic_vcpu __read_mostly; >>> EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); >>> >>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>> +{ >>> + return apic_get_timer_expire(vcpu); >>> +} >>> + >>> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) >>> { >>> struct page *page; >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>> index b1fa8f1..14d6c23 100644 >>> --- a/include/linux/kvm_host.h >>> +++ b/include/linux/kvm_host.h >>> @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); >>> void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); >>> void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); >>> void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); >>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); >>> >>> void kvm_flush_remote_tlbs(struct kvm *kvm); >>> void kvm_reload_remote_mmus(struct kvm *kvm); >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>> index dd4ac9d..e4bb30b 100644 >>> --- a/virt/kvm/kvm_main.c >>> +++ b/virt/kvm/kvm_main.c >>> @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR); >>> static unsigned int halt_poll_ns_shrink; >>> module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); >>> >>> +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */ >>> +static unsigned int halt_poll_ns_base = 10000; >>> + >>> /* >>> * Ordering of locks: >>> * >>> @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) >>> grow = READ_ONCE(halt_poll_ns_grow); >>> /* 10us base */ >>> if (val == 0 && grow) >>> - val = 10000; >>> + val = halt_poll_ns_base; >>> else >>> val *= grow; >>> >>> @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) >>> ktime_t start, cur; >>> DECLARE_SWAITQUEUE(wait); >>> bool waited = false; >>> - u64 block_ns; >>> + u64 block_ns, delta, remaining; >>> >>> + remaining = kvm_arch_timer_remaining(vcpu); >>> start = cur = ktime_get(); >>> - if (vcpu->halt_poll_ns) { >>> - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); >>> + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { >>> + ktime_t stop; >>> >>> + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining; >>> + stop = ktime_add_ns(ktime_get(), delta); >>> ++vcpu->stat.halt_attempted_poll; >>> do { >>> /* >>> -- >>> 1.9.1 >>> > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
2016-05-20 10:04 GMT+08:00 Yang Zhang <yang.zhang.wz@gmail.com>: > On 2016/5/20 2:36, David Matlack wrote: >> >> On Thu, May 19, 2016 at 11:01 AM, David Matlack <dmatlack@google.com> >> wrote: >>> >>> On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >>>> >>>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>>> >>>> If an emulated lapic timer will fire soon(in the scope of 10us the >>>> base of dynamic halt-polling, lower-end of message passing workload >>>> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >>>> and poll to wait it fire, the fire callback apic_timer_fn() will set >>>> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >>>> This can avoid context switch overhead and the latency which we wake >>>> up vCPU. >>> >>> >>> If I understand correctly, your patch aims to reduce the latency of >>> (APIC Timer expires) -> (Guest resumes execution) using halt-polling. >>> Let me know if I'm misunderstanding. >>> >>> In general, I don't think it makes sense to poll for timer interrupts. >>> We know when the timer interrupt is going to arrive. If we care about >>> the latency of delivering that interrupt to the guest, we should >>> program the hrtimer to wake us up slightly early, and then deliver the >>> virtual timer interrupt right on time (I think KVM's TSC Deadline >>> Timer emulation already does this). >> >> >> (It looks like the way to enable this feature is to set the module >> parameter lapic_timer_advance_ns and make sure your guest is using the >> TSC Deadline timer instead of the APIC Timer.) > > > This feature is slightly different from current advance expiration way. > Advance expiration rely on the VCPU is running(do polling before vmentry). > But in some cases, the timer interrupt may be blocked by other thread(i.e., > IF bit is clear) and VCPU cannot be scheduled to run immediately. So even > advance the timer early, VCPU may still see the latency. But polling is > different, it ensures the VCPU to aware the timer expiration before schedule > out. Great explanation, Yang! I prefer to include this statement in my patch description. > >> >>> I'm curious to know if this scheme >>> would give the same performance improvement to iperf as your patch. >>> >>> We discussed this a bit before on the mailing list before >>> (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling >>> and timer interrupts go in the opposite direction: if the next timer >>> event (from any timer) is less than vcpu->halt_poll_ns, don't poll at >>> all. >>> >>>> >>>> iperf TCP get ~6% bandwidth improvement. >>> >>> >>> Can you explain why your patch results in this bandwidth improvement? > > > It should be reasonable. I have seen the same improvement with ctx switch > benchmark: The latency is reduce from ~2600ns to ~2300ns with the similar > mechanism.(The same idea but different implementation) Good to know it. ;-) Regards, Wanpeng Li > >>> >>>> >>>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>>> Cc: David Matlack <dmatlack@google.com> >>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>>> --- >>>> v1 -> v2: >>>> * add return statement to non-x86 archs >>>> * capture never expire case for x86 (hrtimer is not started) >>>> >>>> arch/arm/include/asm/kvm_host.h | 4 ++++ >>>> arch/arm64/include/asm/kvm_host.h | 4 ++++ >>>> arch/mips/include/asm/kvm_host.h | 4 ++++ >>>> arch/powerpc/include/asm/kvm_host.h | 4 ++++ >>>> arch/s390/include/asm/kvm_host.h | 4 ++++ >>>> arch/x86/kvm/lapic.c | 11 +++++++++++ >>>> arch/x86/kvm/lapic.h | 1 + >>>> arch/x86/kvm/x86.c | 5 +++++ >>>> include/linux/kvm_host.h | 1 + >>>> virt/kvm/kvm_main.c | 14 ++++++++++---- >>>> 10 files changed, 48 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/arch/arm/include/asm/kvm_host.h >>>> b/arch/arm/include/asm/kvm_host.h >>>> index 4cd8732..a5fd858 100644 >>>> --- a/arch/arm/include/asm/kvm_host.h >>>> +++ b/arch/arm/include/asm/kvm_host.h >>>> @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm >>>> *kvm) {} >>>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> static inline void kvm_arm_init_debug(void) {} >>>> static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} >>>> diff --git a/arch/arm64/include/asm/kvm_host.h >>>> b/arch/arm64/include/asm/kvm_host.h >>>> index d49399d..94e227a 100644 >>>> --- a/arch/arm64/include/asm/kvm_host.h >>>> +++ b/arch/arm64/include/asm/kvm_host.h >>>> @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm >>>> *kvm) {} >>>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> void kvm_arm_init_debug(void); >>>> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); >>>> diff --git a/arch/mips/include/asm/kvm_host.h >>>> b/arch/mips/include/asm/kvm_host.h >>>> index 9a37a10..456bc42 100644 >>>> --- a/arch/mips/include/asm/kvm_host.h >>>> +++ b/arch/mips/include/asm/kvm_host.h >>>> @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct >>>> kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> >>>> #endif /* __MIPS_KVM_HOST_H__ */ >>>> diff --git a/arch/powerpc/include/asm/kvm_host.h >>>> b/arch/powerpc/include/asm/kvm_host.h >>>> index ec35af3..5986c79 100644 >>>> --- a/arch/powerpc/include/asm/kvm_host.h >>>> +++ b/arch/powerpc/include/asm/kvm_host.h >>>> @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> #endif /* __POWERPC_KVM_HOST_H__ */ >>>> diff --git a/arch/s390/include/asm/kvm_host.h >>>> b/arch/s390/include/asm/kvm_host.h >>>> index 37b9017..bdb01a1 100644 >>>> --- a/arch/s390/include/asm/kvm_host.h >>>> +++ b/arch/s390/include/asm/kvm_host.h >>>> @@ -696,6 +696,10 @@ static inline void >>>> kvm_arch_flush_shadow_memslot(struct kvm *kvm, >>>> struct kvm_memory_slot *slot) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); >>>> >>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >>>> index bbb5b28..cfeeac3 100644 >>>> --- a/arch/x86/kvm/lapic.c >>>> +++ b/arch/x86/kvm/lapic.c >>>> @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct >>>> kvm_lapic *apic) >>>> return apic->lapic_timer.timer_mode == >>>> APIC_LVT_TIMER_TSCDEADLINE; >>>> } >>>> >>>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) >>>> +{ >>>> + struct kvm_lapic *apic = vcpu->arch.apic; >>>> + struct hrtimer *timer = &apic->lapic_timer.timer; >>>> + >>>> + if (!hrtimer_active(timer)) >>>> + return -1ULL; >>>> + else >>>> + return ktime_to_ns(hrtimer_get_remaining(timer)); >>>> +} >>>> + >>>> static inline int apic_lvt_nmi_mode(u32 lvt_val) >>>> { >>>> return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == >>>> APIC_DM_NMI; >>>> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h >>>> index 891c6da..ee4da6c 100644 >>>> --- a/arch/x86/kvm/lapic.h >>>> +++ b/arch/x86/kvm/lapic.h >>>> @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, >>>> struct kvm_lapic_irq *irq, >>>> struct kvm_vcpu **dest_vcpu); >>>> int kvm_vector_to_index(u32 vector, u32 dest_vcpus, >>>> const unsigned long *bitmap, u32 bitmap_size); >>>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); >>>> #endif >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index a8c7ca3..9b5ad99 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) >>>> struct static_key kvm_no_apic_vcpu __read_mostly; >>>> EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); >>>> >>>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return apic_get_timer_expire(vcpu); >>>> +} >>>> + >>>> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) >>>> { >>>> struct page *page; >>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>>> index b1fa8f1..14d6c23 100644 >>>> --- a/include/linux/kvm_host.h >>>> +++ b/include/linux/kvm_host.h >>>> @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); >>>> void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); >>>> void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); >>>> void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); >>>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); >>>> >>>> void kvm_flush_remote_tlbs(struct kvm *kvm); >>>> void kvm_reload_remote_mmus(struct kvm *kvm); >>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>>> index dd4ac9d..e4bb30b 100644 >>>> --- a/virt/kvm/kvm_main.c >>>> +++ b/virt/kvm/kvm_main.c >>>> @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | >>>> S_IWUSR); >>>> static unsigned int halt_poll_ns_shrink; >>>> module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); >>>> >>>> +/* lower-end of message passing workload latency TCP_RR's poll time < >>>> 10us */ >>>> +static unsigned int halt_poll_ns_base = 10000; >>>> + >>>> /* >>>> * Ordering of locks: >>>> * >>>> @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu >>>> *vcpu) >>>> grow = READ_ONCE(halt_poll_ns_grow); >>>> /* 10us base */ >>>> if (val == 0 && grow) >>>> - val = 10000; >>>> + val = halt_poll_ns_base; >>>> else >>>> val *= grow; >>>> >>>> @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) >>>> ktime_t start, cur; >>>> DECLARE_SWAITQUEUE(wait); >>>> bool waited = false; >>>> - u64 block_ns; >>>> + u64 block_ns, delta, remaining; >>>> >>>> + remaining = kvm_arch_timer_remaining(vcpu); >>>> start = cur = ktime_get(); >>>> - if (vcpu->halt_poll_ns) { >>>> - ktime_t stop = ktime_add_ns(ktime_get(), >>>> vcpu->halt_poll_ns); >>>> + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { >>>> + ktime_t stop; >>>> >>>> + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : >>>> remaining; >>>> + stop = ktime_add_ns(ktime_get(), delta); >>>> ++vcpu->stat.halt_attempted_poll; >>>> do { >>>> /* >>>> -- >>>> 1.9.1 >>>> >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > -- > best regards > yang
On Thu, May 19, 2016 at 7:04 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: > On 2016/5/20 2:36, David Matlack wrote: >> >> On Thu, May 19, 2016 at 11:01 AM, David Matlack <dmatlack@google.com> >> wrote: >>> >>> On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >>>> >>>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>>> >>>> If an emulated lapic timer will fire soon(in the scope of 10us the >>>> base of dynamic halt-polling, lower-end of message passing workload >>>> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >>>> and poll to wait it fire, the fire callback apic_timer_fn() will set >>>> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >>>> This can avoid context switch overhead and the latency which we wake >>>> up vCPU. >>> >>> >>> If I understand correctly, your patch aims to reduce the latency of >>> (APIC Timer expires) -> (Guest resumes execution) using halt-polling. >>> Let me know if I'm misunderstanding. >>> >>> In general, I don't think it makes sense to poll for timer interrupts. >>> We know when the timer interrupt is going to arrive. If we care about >>> the latency of delivering that interrupt to the guest, we should >>> program the hrtimer to wake us up slightly early, and then deliver the >>> virtual timer interrupt right on time (I think KVM's TSC Deadline >>> Timer emulation already does this). >> >> >> (It looks like the way to enable this feature is to set the module >> parameter lapic_timer_advance_ns and make sure your guest is using the >> TSC Deadline timer instead of the APIC Timer.) > > > This feature is slightly different from current advance expiration way. > Advance expiration rely on the VCPU is running(do polling before vmentry). > But in some cases, the timer interrupt may be blocked by other thread(i.e., > IF bit is clear) and VCPU cannot be scheduled to run immediately. So even > advance the timer early, VCPU may still see the latency. But polling is > different, it ensures the VCPU to aware the timer expiration before schedule > out. > >> >>> I'm curious to know if this scheme >>> would give the same performance improvement to iperf as your patch. >>> >>> We discussed this a bit before on the mailing list before >>> (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling >>> and timer interrupts go in the opposite direction: if the next timer >>> event (from any timer) is less than vcpu->halt_poll_ns, don't poll at >>> all. >>> >>>> >>>> iperf TCP get ~6% bandwidth improvement. >>> >>> >>> Can you explain why your patch results in this bandwidth improvement? > > > It should be reasonable. I have seen the same improvement with ctx switch > benchmark: The latency is reduce from ~2600ns to ~2300ns with the similar > mechanism.(The same idea but different implementation) It's not obvious to me why polling for a timer interrupt would improve context switch latency. Can you explain a bit more? > >>> >>>> >>>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>>> Cc: David Matlack <dmatlack@google.com> >>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>>> --- >>>> v1 -> v2: >>>> * add return statement to non-x86 archs >>>> * capture never expire case for x86 (hrtimer is not started) >>>> >>>> arch/arm/include/asm/kvm_host.h | 4 ++++ >>>> arch/arm64/include/asm/kvm_host.h | 4 ++++ >>>> arch/mips/include/asm/kvm_host.h | 4 ++++ >>>> arch/powerpc/include/asm/kvm_host.h | 4 ++++ >>>> arch/s390/include/asm/kvm_host.h | 4 ++++ >>>> arch/x86/kvm/lapic.c | 11 +++++++++++ >>>> arch/x86/kvm/lapic.h | 1 + >>>> arch/x86/kvm/x86.c | 5 +++++ >>>> include/linux/kvm_host.h | 1 + >>>> virt/kvm/kvm_main.c | 14 ++++++++++---- >>>> 10 files changed, 48 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/arch/arm/include/asm/kvm_host.h >>>> b/arch/arm/include/asm/kvm_host.h >>>> index 4cd8732..a5fd858 100644 >>>> --- a/arch/arm/include/asm/kvm_host.h >>>> +++ b/arch/arm/include/asm/kvm_host.h >>>> @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm >>>> *kvm) {} >>>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> static inline void kvm_arm_init_debug(void) {} >>>> static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} >>>> diff --git a/arch/arm64/include/asm/kvm_host.h >>>> b/arch/arm64/include/asm/kvm_host.h >>>> index d49399d..94e227a 100644 >>>> --- a/arch/arm64/include/asm/kvm_host.h >>>> +++ b/arch/arm64/include/asm/kvm_host.h >>>> @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm >>>> *kvm) {} >>>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> void kvm_arm_init_debug(void); >>>> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); >>>> diff --git a/arch/mips/include/asm/kvm_host.h >>>> b/arch/mips/include/asm/kvm_host.h >>>> index 9a37a10..456bc42 100644 >>>> --- a/arch/mips/include/asm/kvm_host.h >>>> +++ b/arch/mips/include/asm/kvm_host.h >>>> @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct >>>> kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> >>>> #endif /* __MIPS_KVM_HOST_H__ */ >>>> diff --git a/arch/powerpc/include/asm/kvm_host.h >>>> b/arch/powerpc/include/asm/kvm_host.h >>>> index ec35af3..5986c79 100644 >>>> --- a/arch/powerpc/include/asm/kvm_host.h >>>> +++ b/arch/powerpc/include/asm/kvm_host.h >>>> @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> #endif /* __POWERPC_KVM_HOST_H__ */ >>>> diff --git a/arch/s390/include/asm/kvm_host.h >>>> b/arch/s390/include/asm/kvm_host.h >>>> index 37b9017..bdb01a1 100644 >>>> --- a/arch/s390/include/asm/kvm_host.h >>>> +++ b/arch/s390/include/asm/kvm_host.h >>>> @@ -696,6 +696,10 @@ static inline void >>>> kvm_arch_flush_shadow_memslot(struct kvm *kvm, >>>> struct kvm_memory_slot *slot) {} >>>> static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} >>>> static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} >>>> +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return -1ULL; >>>> +} >>>> >>>> void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); >>>> >>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >>>> index bbb5b28..cfeeac3 100644 >>>> --- a/arch/x86/kvm/lapic.c >>>> +++ b/arch/x86/kvm/lapic.c >>>> @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct >>>> kvm_lapic *apic) >>>> return apic->lapic_timer.timer_mode == >>>> APIC_LVT_TIMER_TSCDEADLINE; >>>> } >>>> >>>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) >>>> +{ >>>> + struct kvm_lapic *apic = vcpu->arch.apic; >>>> + struct hrtimer *timer = &apic->lapic_timer.timer; >>>> + >>>> + if (!hrtimer_active(timer)) >>>> + return -1ULL; >>>> + else >>>> + return ktime_to_ns(hrtimer_get_remaining(timer)); >>>> +} >>>> + >>>> static inline int apic_lvt_nmi_mode(u32 lvt_val) >>>> { >>>> return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == >>>> APIC_DM_NMI; >>>> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h >>>> index 891c6da..ee4da6c 100644 >>>> --- a/arch/x86/kvm/lapic.h >>>> +++ b/arch/x86/kvm/lapic.h >>>> @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, >>>> struct kvm_lapic_irq *irq, >>>> struct kvm_vcpu **dest_vcpu); >>>> int kvm_vector_to_index(u32 vector, u32 dest_vcpus, >>>> const unsigned long *bitmap, u32 bitmap_size); >>>> +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); >>>> #endif >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index a8c7ca3..9b5ad99 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) >>>> struct static_key kvm_no_apic_vcpu __read_mostly; >>>> EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); >>>> >>>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) >>>> +{ >>>> + return apic_get_timer_expire(vcpu); >>>> +} >>>> + >>>> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) >>>> { >>>> struct page *page; >>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>>> index b1fa8f1..14d6c23 100644 >>>> --- a/include/linux/kvm_host.h >>>> +++ b/include/linux/kvm_host.h >>>> @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); >>>> void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); >>>> void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); >>>> void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); >>>> +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); >>>> >>>> void kvm_flush_remote_tlbs(struct kvm *kvm); >>>> void kvm_reload_remote_mmus(struct kvm *kvm); >>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>>> index dd4ac9d..e4bb30b 100644 >>>> --- a/virt/kvm/kvm_main.c >>>> +++ b/virt/kvm/kvm_main.c >>>> @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | >>>> S_IWUSR); >>>> static unsigned int halt_poll_ns_shrink; >>>> module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); >>>> >>>> +/* lower-end of message passing workload latency TCP_RR's poll time < >>>> 10us */ >>>> +static unsigned int halt_poll_ns_base = 10000; >>>> + >>>> /* >>>> * Ordering of locks: >>>> * >>>> @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu >>>> *vcpu) >>>> grow = READ_ONCE(halt_poll_ns_grow); >>>> /* 10us base */ >>>> if (val == 0 && grow) >>>> - val = 10000; >>>> + val = halt_poll_ns_base; >>>> else >>>> val *= grow; >>>> >>>> @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) >>>> ktime_t start, cur; >>>> DECLARE_SWAITQUEUE(wait); >>>> bool waited = false; >>>> - u64 block_ns; >>>> + u64 block_ns, delta, remaining; >>>> >>>> + remaining = kvm_arch_timer_remaining(vcpu); >>>> start = cur = ktime_get(); >>>> - if (vcpu->halt_poll_ns) { >>>> - ktime_t stop = ktime_add_ns(ktime_get(), >>>> vcpu->halt_poll_ns); >>>> + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { >>>> + ktime_t stop; >>>> >>>> + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : >>>> remaining; >>>> + stop = ktime_add_ns(ktime_get(), delta); >>>> ++vcpu->stat.halt_attempted_poll; >>>> do { >>>> /* >>>> -- >>>> 1.9.1 >>>> >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > -- > best regards > yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2016/5/21 2:37, David Matlack wrote: > On Thu, May 19, 2016 at 7:04 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: >> On 2016/5/20 2:36, David Matlack wrote: >>> >>> On Thu, May 19, 2016 at 11:01 AM, David Matlack <dmatlack@google.com> >>> wrote: >>>> >>>> On Thu, May 19, 2016 at 6:27 AM, Wanpeng Li <kernellwp@gmail.com> wrote: >>>>> >>>>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>>>> >>>>> If an emulated lapic timer will fire soon(in the scope of 10us the >>>>> base of dynamic halt-polling, lower-end of message passing workload >>>>> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >>>>> and poll to wait it fire, the fire callback apic_timer_fn() will set >>>>> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >>>>> This can avoid context switch overhead and the latency which we wake >>>>> up vCPU. >>>> >>>> >>>> If I understand correctly, your patch aims to reduce the latency of >>>> (APIC Timer expires) -> (Guest resumes execution) using halt-polling. >>>> Let me know if I'm misunderstanding. >>>> >>>> In general, I don't think it makes sense to poll for timer interrupts. >>>> We know when the timer interrupt is going to arrive. If we care about >>>> the latency of delivering that interrupt to the guest, we should >>>> program the hrtimer to wake us up slightly early, and then deliver the >>>> virtual timer interrupt right on time (I think KVM's TSC Deadline >>>> Timer emulation already does this). >>> >>> >>> (It looks like the way to enable this feature is to set the module >>> parameter lapic_timer_advance_ns and make sure your guest is using the >>> TSC Deadline timer instead of the APIC Timer.) >> >> >> This feature is slightly different from current advance expiration way. >> Advance expiration rely on the VCPU is running(do polling before vmentry). >> But in some cases, the timer interrupt may be blocked by other thread(i.e., >> IF bit is clear) and VCPU cannot be scheduled to run immediately. So even >> advance the timer early, VCPU may still see the latency. But polling is >> different, it ensures the VCPU to aware the timer expiration before schedule >> out. >> >>> >>>> I'm curious to know if this scheme >>>> would give the same performance improvement to iperf as your patch. >>>> >>>> We discussed this a bit before on the mailing list before >>>> (https://lkml.org/lkml/2016/3/29/680). I'd like to see halt-polling >>>> and timer interrupts go in the opposite direction: if the next timer >>>> event (from any timer) is less than vcpu->halt_poll_ns, don't poll at >>>> all. >>>> >>>>> >>>>> iperf TCP get ~6% bandwidth improvement. >>>> >>>> >>>> Can you explain why your patch results in this bandwidth improvement? >> >> >> It should be reasonable. I have seen the same improvement with ctx switch >> benchmark: The latency is reduce from ~2600ns to ~2300ns with the similar >> mechanism.(The same idea but different implementation) > > It's not obvious to me why polling for a timer interrupt would improve > context switch latency. Can you explain a bit more? We have a workload which using high resolution timer(less than 1ms) inside guest. It rely on the timer to wakeup itself. Sometimes the timer is expected to fired just after the VCPU is blocked due to execute halt instruction. But the thread who is running in the CPU will turn off the hardware interrupt for long time due to disk access. This will cause the timer interrupt been blocked until the interrupt is re-open. For optimization, we let VCPU to poll for a while if the next timer will arrive soon before schedule out. And the result shows good when running several workloads inside guest.
On Sun, May 22, 2016 at 6:26 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: > On 2016/5/21 2:37, David Matlack wrote: >> >> It's not obvious to me why polling for a timer interrupt would improve >> context switch latency. Can you explain a bit more? > > > We have a workload which using high resolution timer(less than 1ms) inside > guest. It rely on the timer to wakeup itself. Sometimes the timer is > expected to fired just after the VCPU is blocked due to execute halt > instruction. But the thread who is running in the CPU will turn off the > hardware interrupt for long time due to disk access. This will cause the > timer interrupt been blocked until the interrupt is re-open. Does this happen on the idle thread (swapper)? If not, halt-polling may not help; it only polls if there are no other runnable threads. > For optimization, we let VCPU to poll for a while if the next timer will > arrive soon before schedule out. And the result shows good when running > several workloads inside guest. Thanks for the explanation, I appreciate it. > > -- > best regards > yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2016/5/24 2:04, David Matlack wrote: > On Sun, May 22, 2016 at 6:26 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: >> On 2016/5/21 2:37, David Matlack wrote: >>> >>> It's not obvious to me why polling for a timer interrupt would improve >>> context switch latency. Can you explain a bit more? >> >> >> We have a workload which using high resolution timer(less than 1ms) inside >> guest. It rely on the timer to wakeup itself. Sometimes the timer is >> expected to fired just after the VCPU is blocked due to execute halt >> instruction. But the thread who is running in the CPU will turn off the >> hardware interrupt for long time due to disk access. This will cause the >> timer interrupt been blocked until the interrupt is re-open. > > Does this happen on the idle thread (swapper)? If not, halt-polling > may not help; it only polls if there are no other runnable threads. Yes, there is no runnable task inside guest. > >> For optimization, we let VCPU to poll for a while if the next timer will >> arrive soon before schedule out. And the result shows good when running >> several workloads inside guest. > > Thanks for the explanation, I appreciate it. > >> >> -- >> best regards >> yang
On Mon, May 23, 2016 at 6:13 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: > On 2016/5/24 2:04, David Matlack wrote: >> >> On Sun, May 22, 2016 at 6:26 PM, Yang Zhang <yang.zhang.wz@gmail.com> >> wrote: >>> >>> On 2016/5/21 2:37, David Matlack wrote: >>>> >>>> >>>> It's not obvious to me why polling for a timer interrupt would improve >>>> context switch latency. Can you explain a bit more? >>> >>> >>> >>> We have a workload which using high resolution timer(less than 1ms) >>> inside >>> guest. It rely on the timer to wakeup itself. Sometimes the timer is >>> expected to fired just after the VCPU is blocked due to execute halt >>> instruction. But the thread who is running in the CPU will turn off the >>> hardware interrupt for long time due to disk access. This will cause the >>> timer interrupt been blocked until the interrupt is re-open. >> >> >> Does this happen on the idle thread (swapper)? If not, halt-polling >> may not help; it only polls if there are no other runnable threads. > > > Yes, there is no runnable task inside guest. Sorry for the confusion, my question was about the host, not the guest. Halt-polling only polls if there are no other runnable threads on the host CPU (see the check for single_task_running() in kvm_vcpu_block()). > > >> >>> For optimization, we let VCPU to poll for a while if the next timer will >>> arrive soon before schedule out. And the result shows good when running >>> several workloads inside guest. >> >> >> Thanks for the explanation, I appreciate it. >> >>> >>> -- >>> best regards >>> yang > > > > -- > best regards > yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2016/5/24 9:16, David Matlack wrote: > On Mon, May 23, 2016 at 6:13 PM, Yang Zhang <yang.zhang.wz@gmail.com> wrote: >> On 2016/5/24 2:04, David Matlack wrote: >>> >>> On Sun, May 22, 2016 at 6:26 PM, Yang Zhang <yang.zhang.wz@gmail.com> >>> wrote: >>>> >>>> On 2016/5/21 2:37, David Matlack wrote: >>>>> >>>>> >>>>> It's not obvious to me why polling for a timer interrupt would improve >>>>> context switch latency. Can you explain a bit more? >>>> >>>> >>>> >>>> We have a workload which using high resolution timer(less than 1ms) >>>> inside >>>> guest. It rely on the timer to wakeup itself. Sometimes the timer is >>>> expected to fired just after the VCPU is blocked due to execute halt >>>> instruction. But the thread who is running in the CPU will turn off the >>>> hardware interrupt for long time due to disk access. This will cause the >>>> timer interrupt been blocked until the interrupt is re-open. >>> >>> >>> Does this happen on the idle thread (swapper)? If not, halt-polling >>> may not help; it only polls if there are no other runnable threads. >> >> >> Yes, there is no runnable task inside guest. > > Sorry for the confusion, my question was about the host, not the > guest. Halt-polling only polls if there are no other runnable threads > on the host CPU (see the check for single_task_running() in > kvm_vcpu_block()). ok, i see your point. I didn't check it before. But i have observed that the host CPU may wake up immediately after entering the power idle. Then another task takes the CPU until the schedule signal arrived. And this will cause timer injection delay by several ms. > >> >> >>> >>>> For optimization, we let VCPU to poll for a while if the next timer will >>>> arrive soon before schedule out. And the result shows good when running >>>> several workloads inside guest. >>> >>> >>> Thanks for the explanation, I appreciate it. >>> >>>> >>>> -- >>>> best regards >>>> yang >> >> >> >> -- >> best regards >> yang
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h index 4cd8732..a5fd858 100644 --- a/arch/arm/include/asm/kvm_host.h +++ b/arch/arm/include/asm/kvm_host.h @@ -284,6 +284,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return -1ULL; +} static inline void kvm_arm_init_debug(void) {} static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {} diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index d49399d..94e227a 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -359,6 +359,10 @@ static inline void kvm_arch_sync_events(struct kvm *kvm) {} static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return -1ULL; +} void kvm_arm_init_debug(void); void kvm_arm_setup_debug(struct kvm_vcpu *vcpu); diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index 9a37a10..456bc42 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -813,6 +813,10 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {} static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return -1ULL; +} static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} #endif /* __MIPS_KVM_HOST_H__ */ diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index ec35af3..5986c79 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -729,5 +729,9 @@ static inline void kvm_arch_exit(void) {} static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return -1ULL; +} #endif /* __POWERPC_KVM_HOST_H__ */ diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index 37b9017..bdb01a1 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -696,6 +696,10 @@ static inline void kvm_arch_flush_shadow_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) {} static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} +static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return -1ULL; +} void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu); diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index bbb5b28..cfeeac3 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -256,6 +256,17 @@ static inline int apic_lvtt_tscdeadline(struct kvm_lapic *apic) return apic->lapic_timer.timer_mode == APIC_LVT_TIMER_TSCDEADLINE; } +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu) +{ + struct kvm_lapic *apic = vcpu->arch.apic; + struct hrtimer *timer = &apic->lapic_timer.timer; + + if (!hrtimer_active(timer)) + return -1ULL; + else + return ktime_to_ns(hrtimer_get_remaining(timer)); +} + static inline int apic_lvt_nmi_mode(u32 lvt_val) { return (lvt_val & (APIC_MODE_MASK | APIC_LVT_MASKED)) == APIC_DM_NMI; diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 891c6da..ee4da6c 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -212,4 +212,5 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, struct kvm_vcpu **dest_vcpu); int kvm_vector_to_index(u32 vector, u32 dest_vcpus, const unsigned long *bitmap, u32 bitmap_size); +u64 apic_get_timer_expire(struct kvm_vcpu *vcpu); #endif diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a8c7ca3..9b5ad99 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7623,6 +7623,11 @@ bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) struct static_key kvm_no_apic_vcpu __read_mostly; EXPORT_SYMBOL_GPL(kvm_no_apic_vcpu); +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) +{ + return apic_get_timer_expire(vcpu); +} + int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) { struct page *page; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index b1fa8f1..14d6c23 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -663,6 +663,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target); void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu); void kvm_load_guest_fpu(struct kvm_vcpu *vcpu); void kvm_put_guest_fpu(struct kvm_vcpu *vcpu); +u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu); void kvm_flush_remote_tlbs(struct kvm *kvm); void kvm_reload_remote_mmus(struct kvm *kvm); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index dd4ac9d..e4bb30b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR); static unsigned int halt_poll_ns_shrink; module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR); +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */ +static unsigned int halt_poll_ns_base = 10000; + /* * Ordering of locks: * @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) grow = READ_ONCE(halt_poll_ns_grow); /* 10us base */ if (val == 0 && grow) - val = 10000; + val = halt_poll_ns_base; else val *= grow; @@ -2014,12 +2017,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) ktime_t start, cur; DECLARE_SWAITQUEUE(wait); bool waited = false; - u64 block_ns; + u64 block_ns, delta, remaining; + remaining = kvm_arch_timer_remaining(vcpu); start = cur = ktime_get(); - if (vcpu->halt_poll_ns) { - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); + if (vcpu->halt_poll_ns || remaining < halt_poll_ns_base) { + ktime_t stop; + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining; + stop = ktime_add_ns(ktime_get(), delta); ++vcpu->stat.halt_attempted_poll; do { /*