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

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Date:   Fri, 10 Apr 2020 17:17:23 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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 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,

Paolo