linux-kernel - Re: [PATCH 2/2] KVM: X86: Implement PV send IPI support

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Date:   Sat, 30 Jun 2018 18:04:47 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 2/2] KVM: X86: Implement PV send IPI support

On Fri, 29 Jun 2018 at 18:45, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 29/06/2018 11:51, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Using hypercall to send IPIs by one vmexit instead of one by one for
> > xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster
> > mode.
> >
> > Even if enable qemu interrupt remapping and PV TLB Shootdown, I can still
> > observe ~14% performance boost by ebizzy benchmark for 64 vCPUs VM, the
> > total msr-induced vmexits reduce ~70%.
> >
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  Documentation/virtual/kvm/cpuid.txt |  4 ++++
> >  arch/x86/kvm/cpuid.c                |  3 ++-
> >  arch/x86/kvm/x86.c                  | 25 +++++++++++++++++++++++++
> >  include/uapi/linux/kvm_para.h       |  1 +
> >  4 files changed, 32 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> > index ab022dc..d72359f 100644
> > --- a/Documentation/virtual/kvm/cpuid.txt
> > +++ b/Documentation/virtual/kvm/cpuid.txt
> > @@ -62,6 +62,10 @@ KVM_FEATURE_ASYNC_PF_VMEXIT        ||    10 || paravirtualized async PF VM exit
> >                                     ||       || can be enabled by setting bit 2
> >                                     ||       || when writing to msr 0x4b564d02
> >  ------------------------------------------------------------------------------
> > +KVM_FEATURE_PV_SEND_IPI            ||    11 || guest checks this feature bit
> > +                                   ||       || before enabling paravirtualized
> > +                                   ||       || send IPIs.
>
> It's not "enabling" but "using".  You also need to document the
> hypercall itself.

Will fix it in v2.

Regards,
Wanpeng Li