Re: [PATCH] KVM: Boosting vCPUs that are delivering interrupts

[Wanpeng Li]

Cc arm and powerpc people,
On Mon, 15 Jul 2019 at 18:53, Christian Borntraeger
<borntraeger@xxxxxxxxxx> wrote:
>
>
>
> On 12.07.19 09:10, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> >
> > Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during vcpu wakeup
> > and interrupt delivery), except the lock holder, we want to also boost vCPUs
> > that are delivering interrupts. Actually most smp_call_function_many calls are
> > synchronous ipi calls, the ipi target vCPUs are also good yield candidates.
> > This patch sets preempted flag during wakeup and interrupt delivery time.
> >
> > Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM:
> > ebizzy -M
> >
> >             vanilla     boosting    improved
> > 1VM          23000       21232        -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       55%
> >
> > w/ boosting + w/ pv sched yield(vanilla)
> >
> >                       vanilla     boosting   improved
> >              1844         5157       79%
> >
> > 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
> This certainly made sense for s390 so I guess that this also makes sense
> for others.
> Nnote we (s390) do not use kvm_vcpu_kick, so this should not cause
> any issue for s390.
>
>
> >
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > ---
> >  virt/kvm/kvm_main.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index b4ab59d..2c46705 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2404,8 +2404,10 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
> >       int me;
> >       int cpu = vcpu->cpu;
> >
> > -     if (kvm_vcpu_wake_up(vcpu))
> > +     if (kvm_vcpu_wake_up(vcpu)) {
> > +             vcpu->preempted = true;
> >               return;
> > +     }
> >
> >       me = get_cpu();
> >       if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
> >
>