linux-kernel - Re: [PATCH v2 1/2] KVM: VMX: FIXED+PHYSICAL mode single target IPI fastpath

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Message-ID: <CANRm+Cw6vKHnfq4G0wmKmbs63vXbVGtPBPpxZBzr1JL+HTaYGQ@mail.gmail.com>
Date:   Wed, 20 Nov 2019 08:24:45 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 1/2] KVM: VMX: FIXED+PHYSICAL mode single target IPI fastpath

On Wed, 20 Nov 2019 at 02:36, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
[...]
>
> From 1ea8ff1aa766928c869ef7c1eb437fe4f7b8daf9 Mon Sep 17 00:00:00 2001
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> Date: Tue, 19 Nov 2019 09:50:42 -0800
> Subject: [PATCH] KVM: x86: Add a fast path for sending virtual IPIs in x2APIC
>  mode
>
> Add a fast path to handle writes to the ICR when the local APIC is
> emulated in the kernel and x2APIC is enabled.  The fast path is invoked
> at ->handle_exit_irqoff() to emulate only the effect of the ICR write
> itself, i.e. the sending of IPIs.  Sending IPIs early in the VM-Exit
> flow reduces the latency of virtual IPIs by avoiding the expensive bits
> of transitioning from guest to host, e.g. reacquiring KVM's SRCU lock.
>
> Suggested-by: Wanpeng Li <wanpengli@...cent.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>

Hmm, I welcome the idea to improve the original patch, but this is too
much for me. :(