| Message ID | 1562376411-3533-2-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: LAPIC: Implement Exitless Timer | expand |
On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the > lapic timer to avoid to wait until the next kvm exit for the guest to > see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick > after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned > will be used in follow up patches. > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Marcelo Tosatti <mtosatti@redhat.com> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kvm/lapic.c | 8 ++++---- > arch/x86/kvm/x86.c | 6 +----- > 2 files changed, 5 insertions(+), 9 deletions(-) ... > @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) > > timer = &vcpu->arch.apic->lapic_timer.timer; > if (hrtimer_cancel(timer)) > - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED); > + hrtimer_start_expires(timer, HRTIMER_MODE_ABS); > } > > /* Wait, in that case why are we even bothering to cancel and restart the timer? I thought the whole point of that was to pin it to the *new* CPU that this vCPU is running on. If not, can't we just kill __kvm_migrate_apic_timer() off completely not?
On Wed, Mar 09, 2022 at 10:26:51AM +0100, David Woodhouse wrote: > On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote: > > From: Wanpeng Li <wanpengli@tencent.com> > > > > Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the > > lapic timer to avoid to wait until the next kvm exit for the guest to > > see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick > > after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned > > will be used in follow up patches. > > > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: Radim Krčmář <rkrcmar@redhat.com> > > Cc: Marcelo Tosatti <mtosatti@redhat.com> > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > --- > > arch/x86/kvm/lapic.c | 8 ++++---- > > arch/x86/kvm/x86.c | 6 +----- > > 2 files changed, 5 insertions(+), 9 deletions(-) > > ... > > > > @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) > > > > timer = &vcpu->arch.apic->lapic_timer.timer; > > if (hrtimer_cancel(timer)) > > - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED); > > + hrtimer_start_expires(timer, HRTIMER_MODE_ABS); > > } > > > > /* > > Wait, in that case why are we even bothering to cancel and restart the > timer? I thought the whole point of that was to pin it to the *new* CPU > that this vCPU is running on. > > If not, can't we just kill __kvm_migrate_apic_timer() off completely > not? Current code looks like this: void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) { struct hrtimer *timer; if (!lapic_in_kernel(vcpu) || kvm_can_post_timer_interrupt(vcpu)) <---------- return; timer = &vcpu->arch.apic->lapic_timer.timer; if (hrtimer_cancel(timer)) hrtimer_start_expires(timer, HRTIMER_MODE_ABS_HARD); } Yeah, should be HRTIMER_MODE_ABS_PINNED AFAICS.
On Wed, 2022-03-09 at 08:24 -0300, Marcelo Tosatti wrote: > On Wed, Mar 09, 2022 at 10:26:51AM +0100, David Woodhouse wrote: > > On Sat, 2019-07-06 at 09:26 +0800, Wanpeng Li wrote: > > > From: Wanpeng Li <wanpengli@tencent.com> > > > > > > Commit 61abdbe0bcc2 ("kvm: x86: make lapic hrtimer pinned") pinned the > > > lapic timer to avoid to wait until the next kvm exit for the guest to > > > see KVM_REQ_PENDING_TIMER set. There is another solution to give a kick > > > after setting the KVM_REQ_PENDING_TIMER bit, make lapic timer unpinned > > > will be used in follow up patches. > > > > > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > > Cc: Radim Krčmář <rkrcmar@redhat.com> > > > Cc: Marcelo Tosatti <mtosatti@redhat.com> > > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > > --- > > > arch/x86/kvm/lapic.c | 8 ++++---- > > > arch/x86/kvm/x86.c | 6 +----- > > > 2 files changed, 5 insertions(+), 9 deletions(-) > > > > ... > > > > > > > @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) > > > > > > timer = &vcpu->arch.apic->lapic_timer.timer; > > > if (hrtimer_cancel(timer)) > > > - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED); > > > + hrtimer_start_expires(timer, HRTIMER_MODE_ABS); > > > } > > > > > > /* > > > > Wait, in that case why are we even bothering to cancel and restart the > > timer? I thought the whole point of that was to pin it to the *new* CPU > > that this vCPU is running on. > > > > If not, can't we just kill __kvm_migrate_apic_timer() off completely > > not? > > Current code looks like this: > > void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) > { > struct hrtimer *timer; > > if (!lapic_in_kernel(vcpu) || > kvm_can_post_timer_interrupt(vcpu)) <---------- > return; > > timer = &vcpu->arch.apic->lapic_timer.timer; > if (hrtimer_cancel(timer)) > hrtimer_start_expires(timer, HRTIMER_MODE_ABS_HARD); > } > > Yeah, should be HRTIMER_MODE_ABS_PINNED AFAICS. No, it's *intentionally* not pinned any more, since this patch that I'm replying to, which became commit 4d151bf3b89. It doesn't *have* to run on the same physical CPU, because of the epiphany that it can just call kvm_vcpu_kick() after making the request. But if it's a recurring timer it's still *best* for it to run on the same physical CPU, just for cache locality reasons. So I think I was wrong; the migration *isn't* pointless. It's still a valid optimisation; it's just not *mandatory* any more.
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 459d1ee..707ca9c 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1582,7 +1582,7 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic) likely(ns > apic->lapic_timer.timer_advance_ns)) { expire = ktime_add_ns(now, ns); expire = ktime_sub_ns(expire, ktimer->timer_advance_ns); - hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS_PINNED); + hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS); } else apic_timer_expired(apic); @@ -1684,7 +1684,7 @@ static void start_sw_period(struct kvm_lapic *apic) hrtimer_start(&apic->lapic_timer.timer, apic->lapic_timer.target_expiration, - HRTIMER_MODE_ABS_PINNED); + HRTIMER_MODE_ABS); } bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu) @@ -2321,7 +2321,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns) apic->vcpu = vcpu; hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC, - HRTIMER_MODE_ABS_PINNED); + HRTIMER_MODE_ABS); apic->lapic_timer.timer.function = apic_timer_fn; if (timer_advance_ns == -1) { apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; @@ -2510,7 +2510,7 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu) timer = &vcpu->arch.apic->lapic_timer.timer; if (hrtimer_cancel(timer)) - hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED); + hrtimer_start_expires(timer, HRTIMER_MODE_ABS); } /* diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3a7cd935..e199ac7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1437,12 +1437,8 @@ static void update_pvclock_gtod(struct timekeeper *tk) void kvm_set_pending_timer(struct kvm_vcpu *vcpu) { - /* - * Note: KVM_REQ_PENDING_TIMER is implicitly checked in - * vcpu_enter_guest. This function is only called from - * the physical CPU that is running vcpu. - */ kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu); + kvm_vcpu_kick(vcpu); } static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)