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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Mon, 26 Apr 2021 11:02:19 +0800
Message-ID: <CANRm+CzoS=HhiHg6w6dy8P+r3POeP3uMZqFvJr4oHMa1aNJqxg@mail.gmail.com>
Subject: Re: [RFC PATCH 0/2] Mitigating Excessive Pause-Loop Exiting in
 VM-Agnostic KVM
To:     Kenta Ishiguro <kentaishiguro@sslab.ics.keio.ac.jp>
Cc:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Hildenbrand <david@redhat.com>,
        kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Pierre-Louis Aublin <pl@sslab.ics.keio.ac.jp>,
        =?UTF-8?B?5rKz6YeO5YGl5LqM?= <kono@sslab.ics.keio.ac.jp>
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On Mon, 26 Apr 2021 at 10:56, Kenta Ishiguro
<kentaishiguro@sslab.ics.keio.ac.jp> wrote:
>
> Dear all,
>
> Thank you for the insightful feedback.
>
> Does Sean's suggested version of Wanpeng's patch mark a running vCPU as an IPI
> receiver? If it's right, I think the candidate set of vCPUs for boost is
> slightly different between using kvm_arch_interrupt_delivery and using boolean
> ipi_received. In the version of using boolean ipi_received, vCPUs which
> receive IPI while running are also candidates for a boost.
> However, they likely have already responded to their IPI before they exit.

             if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
+                !READ_ONCE(vcpu->ipi_received) &&

There is a vcpu->preempted checking here.

    Wanpeng