linux-kernel - Re: [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery

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Message-ID: <CANRm+CyeH_qNs2oJPVT4Lnw9VB-+86QkLiLVy25OtK=k44CBsg@mail.gmail.com>
Date:   Tue, 12 Nov 2019 09:34:34 +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 Krčmář <rkrcmar@...hat.com>,
        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>
Subject: Re: [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery

On Tue, 12 Nov 2019 at 05:59, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 09/11/19 08:05, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > After disabling mwait/halt/pause vmexits, RESCHEDULE_VECTOR and
> > CALL_FUNCTION_SINGLE_VECTOR etc IPI is one of the main remaining
> > cause of vmexits observed in product environment which can't be
> > optimized by PV IPIs. This patch is the follow-up on commit
> > 0e6d242eccdb (KVM: LAPIC: Micro optimize IPI latency), to optimize
> > redundancy logic before fixed mode ipi is delivered in the fast
> > path.
> >
> > - broadcast handling needs to go slow path, so the delivery mode repair
> >   can be delayed to before slow path.
>
> I agree with this part, but is the cost of the irq->shorthand check
> really measurable?

I can drop the second part for v2.

    Wanpeng