linux-kernel - Re: [PATCH v2] KVM: X86: Ultra fast single target IPI fastpath

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Date:   Mon, 13 Apr 2020 09:43:57 +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>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v2] KVM: X86: Ultra fast single target IPI fastpath

On Fri, 10 Apr 2020 at 23:17, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 10/04/20 03:03, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > IPI and Timer cause the main MSRs write vmexits in cloud environment
> > observation, let's optimize virtual IPI latency more aggressively to
> > inject target IPI as soon as possible.
> >
> > Running kvm-unit-tests/vmexit.flat IPI testing on SKX server, disable
> > adaptive advance lapic timer and adaptive halt-polling to avoid the
> > interference, this patch can give another 7% improvement.
> >
> > w/o fastpath -> fastpath            4238 -> 3543  16.4%
> > fastpath     -> ultra fastpath      3543 -> 3293     7%
> > w/o fastpath -> ultra fastpath      4238 -> 3293  22.3%
> >
> > This also revises the performance data in commit 1e9e2622a1 (KVM: VMX:
> > FIXED+PHYSICAL mode single target IPI fastpath), that testing adds
> > --overcommit cpu-pm=on to kvm-unit-tests guest which is unnecessary.
> >
> > Tested-by: Haiwei Li <lihaiwei@...cent.com>
> > Cc: Haiwei Li <lihaiwei@...cent.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > v1 -> v2:
> >  * rebase on latest kvm/queue
> >  * update patch description
> >
> >  arch/x86/include/asm/kvm_host.h |  6 +++---
> >  arch/x86/kvm/svm/svm.c          | 21 ++++++++++++++-------
> >  arch/x86/kvm/vmx/vmx.c          | 19 +++++++++++++------
> >  arch/x86/kvm/x86.c              |  4 ++--
> >  4 files changed, 32 insertions(+), 18 deletions(-)
>
> That's less ugly than I expected. :D  I'll queue it in the next week or
> so.  But even though the commit subject is cool, I'll change it to "KVM:
> x86: move IPI fastpath inside kvm_x86_ops.run".

Thanks.

    Wanpeng