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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Mon, 15 Jul 2019 19:15:36 +0800
Message-ID: <CANRm+Cy=kOR350gegx=oh08nAQvZ+qzvgpqChUat917+wiWh3A@mail.gmail.com>
Subject: Re: [PATCH] KVM: Boosting vCPUs that are delivering interrupts
To:     Christian Borntraeger <borntraeger@de.ibm.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Marc Zyngier <marc.zyngier@arm.com>
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Cc arm and powerpc people,
On Mon, 15 Jul 2019 at 18:53, Christian Borntraeger
<borntraeger@de.ibm.com> wrote:
>
>
>
> On 12.07.19 09:10, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@tencent.com>
> >
> > 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 ca=
lls are
> > synchronous ipi calls, the ipi target vCPUs are also good yield candida=
tes.
> > This patch sets preempted flag during wakeup and interrupt delivery tim=
e.
> >
> > Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RA=
M:
> > 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@redhat.com>
> > Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
> > Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> > ---
> >  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 =3D vcpu->cpu;
> >
> > -     if (kvm_vcpu_wake_up(vcpu))
> > +     if (kvm_vcpu_wake_up(vcpu)) {
> > +             vcpu->preempted =3D true;
> >               return;
> > +     }
> >
> >       me =3D get_cpu();
> >       if (cpu !=3D me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
> >
>