On 18.07.19 15:37, Paolo Bonzini wrote:
> From: Wanpeng Li <[email protected]>
>
> 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 <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Cc: Christian Borntraeger <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: Marc Zyngier <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> 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);
> }
>
>
