| Message ID | 1563457031-21189-2-git-send-email-pbonzini@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Boost vCPUs that are ready to deliver interrupts | expand |
On 18.07.19 15:37, Paolo Bonzini wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during > vcpu wakeup and interrupt delivery), we want to also boost not just > lock holders but also vCPUs that are delivering interrupts. Most > smp_call_function_many calls are synchronous, so the IPI target vCPUs > are also good yield candidates. This patch introduces vcpu->ready to > boost vCPUs during wakeup and interrupt delivery time; unlike s390 we do > not reuse vcpu->preempted so that voluntarily preempted vCPUs are taken > into account by kvm_vcpu_on_spin, but vmx_vcpu_pi_put is not affected > (VT-d PI handles voluntary preemption separately, in pi_pre_block). > > Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM: > ebizzy -M > > vanilla boosting improved > 1VM 21443 23520 9% > 2VM 2800 8000 180% > 3VM 1800 3100 72% > > Testing on my Haswell desktop 8 HT, with 8 vCPUs VM 8GB RAM, two VMs, > one running ebizzy -M, the other running 'stress --cpu 2': > > w/ boosting + w/o pv sched yield(vanilla) > > vanilla boosting improved > 1570 4000 155% > > w/ boosting + w/ pv sched yield(vanilla) > > vanilla boosting improved > 1844 5157 179% > > w/o boosting, perf top in VM: > > 72.33% [kernel] [k] smp_call_function_many > 4.22% [kernel] [k] call_function_i > 3.71% [kernel] [k] async_page_fault > > w/ boosting, perf top in VM: > > 38.43% [kernel] [k] smp_call_function_many > 6.31% [kernel] [k] async_page_fault > 6.13% libc-2.23.so [.] __memcpy_avx_unaligned > 4.88% [kernel] [k] call_function_interrupt > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Christian Borntraeger <borntraeger@de.ibm.com> > Cc: Paul Mackerras <paulus@ozlabs.org> > Cc: Marc Zyngier <maz@kernel.org> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > v2->v3: put it in kvm_vcpu_wake_up, use WRITE_ONCE Looks good. Some more comments > > arch/s390/kvm/interrupt.c | 2 +- > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 9 +++++++-- [...] > @@ -4205,6 +4206,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu) > > if (vcpu->preempted) > vcpu->preempted = false; > + if (vcpu->ready) > + WRITE_ONCE(vcpu->ready, false); What is the rationale of checking before writing. Avoiding writable cache line ping pong? > > kvm_arch_sched_in(vcpu, cpu); > > @@ -4216,8 +4219,10 @@ static void kvm_sched_out(struct preempt_notifier *pn, > { > struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); > > - if (current->state == TASK_RUNNING) > + if (current->state == TASK_RUNNING) { > vcpu->preempted = true; WOuld it make sense to also use WRITE_ONCE for vcpu->preempted ? > + WRITE_ONCE(vcpu->ready, true); > + } > kvm_arch_vcpu_put(vcpu); > } > >
On 18/07/19 15:45, Christian Borntraeger wrote: > > > On 18.07.19 15:37, Paolo Bonzini wrote: >> From: Wanpeng Li <wanpengli@tencent.com> >> >> Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during >> vcpu wakeup and interrupt delivery), we want to also boost not just >> lock holders but also vCPUs that are delivering interrupts. Most >> smp_call_function_many calls are synchronous, so the IPI target vCPUs >> are also good yield candidates. This patch introduces vcpu->ready to >> boost vCPUs during wakeup and interrupt delivery time; unlike s390 we do >> not reuse vcpu->preempted so that voluntarily preempted vCPUs are taken >> into account by kvm_vcpu_on_spin, but vmx_vcpu_pi_put is not affected >> (VT-d PI handles voluntary preemption separately, in pi_pre_block). >> >> Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM: >> ebizzy -M >> >> vanilla boosting improved >> 1VM 21443 23520 9% >> 2VM 2800 8000 180% >> 3VM 1800 3100 72% >> >> Testing on my Haswell desktop 8 HT, with 8 vCPUs VM 8GB RAM, two VMs, >> one running ebizzy -M, the other running 'stress --cpu 2': >> >> w/ boosting + w/o pv sched yield(vanilla) >> >> vanilla boosting improved >> 1570 4000 155% >> >> w/ boosting + w/ pv sched yield(vanilla) >> >> vanilla boosting improved >> 1844 5157 179% >> >> w/o boosting, perf top in VM: >> >> 72.33% [kernel] [k] smp_call_function_many >> 4.22% [kernel] [k] call_function_i >> 3.71% [kernel] [k] async_page_fault >> >> w/ boosting, perf top in VM: >> >> 38.43% [kernel] [k] smp_call_function_many >> 6.31% [kernel] [k] async_page_fault >> 6.13% libc-2.23.so [.] __memcpy_avx_unaligned >> 4.88% [kernel] [k] call_function_interrupt >> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Radim Krčmář <rkrcmar@redhat.com> >> Cc: Christian Borntraeger <borntraeger@de.ibm.com> >> Cc: Paul Mackerras <paulus@ozlabs.org> >> Cc: Marc Zyngier <maz@kernel.org> >> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> >> --- >> v2->v3: put it in kvm_vcpu_wake_up, use WRITE_ONCE > > > Looks good. Some more comments > >> >> arch/s390/kvm/interrupt.c | 2 +- >> include/linux/kvm_host.h | 1 + >> virt/kvm/kvm_main.c | 9 +++++++-- > [...] > >> @@ -4205,6 +4206,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu) >> >> if (vcpu->preempted) >> vcpu->preempted = false; >> + if (vcpu->ready) >> + WRITE_ONCE(vcpu->ready, false); > > What is the rationale of checking before writing. Avoiding writable cache line ping pong? I think it can be removed. The only case where you'd have ping pong is when vcpu->ready is true due to kvm_vcpu_wake_up, so it's not saving anything. >> kvm_arch_sched_in(vcpu, cpu); >> >> @@ -4216,8 +4219,10 @@ static void kvm_sched_out(struct preempt_notifier *pn, >> { >> struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); >> >> - if (current->state == TASK_RUNNING) >> + if (current->state == TASK_RUNNING) { >> vcpu->preempted = true; > > WOuld it make sense to also use WRITE_ONCE for vcpu->preempted ? vcpu->preempted is not read/written anymore by other threads after this patch. > >> + WRITE_ONCE(vcpu->ready, true); >> + } >> kvm_arch_vcpu_put(vcpu); >> } >> >> >
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c index 9dde4d7d8704..26f8bf4a22a7 100644 --- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -1240,7 +1240,7 @@ void kvm_s390_vcpu_wakeup(struct kvm_vcpu *vcpu) * The vcpu gave up the cpu voluntarily, mark it as a good * yield-candidate. */ - vcpu->preempted = true; + WRITE_ONCE(vcpu->ready, true); swake_up_one(&vcpu->wq); vcpu->stat.halt_wakeup++; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index c5da875f19e3..5c5b5867024c 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -318,6 +318,7 @@ struct kvm_vcpu { } spin_loop; #endif bool preempted; + bool ready; struct kvm_vcpu_arch arch; struct dentry *debugfs_dentry; }; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index b4ab59dd6846..65665e13ab9a 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2387,6 +2387,7 @@ bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu) wqp = kvm_arch_vcpu_wq(vcpu); if (swq_has_sleeper(wqp)) { swake_up_one(wqp); + WRITE_ONCE(vcpu->ready, true); ++vcpu->stat.halt_wakeup; return true; } @@ -2500,7 +2501,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) continue; } else if (pass && i > last_boosted_vcpu) break; - if (!READ_ONCE(vcpu->preempted)) + if (!READ_ONCE(vcpu->ready)) continue; if (vcpu == me) continue; @@ -4205,6 +4206,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu) if (vcpu->preempted) vcpu->preempted = false; + if (vcpu->ready) + WRITE_ONCE(vcpu->ready, false); kvm_arch_sched_in(vcpu, cpu); @@ -4216,8 +4219,10 @@ static void kvm_sched_out(struct preempt_notifier *pn, { struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); - if (current->state == TASK_RUNNING) + if (current->state == TASK_RUNNING) { vcpu->preempted = true; + WRITE_ONCE(vcpu->ready, true); + } kvm_arch_vcpu_put(vcpu); }