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 <20210426031858.12003-1-kentaishiguro@sslab.ics.keio.ac.jp>
In-Reply-To: <20210426031858.12003-1-kentaishiguro@sslab.ics.keio.ac.jp>
From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Mon, 26 Apr 2021 11:58:19 +0800
Message-ID: <CANRm+Cz9GgQFDbbW_3bRO35FwvMGJ-ZFa0rSvEimxFzrvwmpJw@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:     David Hildenbrand <david@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        =?UTF-8?B?5rKz6YeO5YGl5LqM?= <kono@sslab.ics.keio.ac.jp>,
        kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Pierre-Louis Aublin <pl@sslab.ics.keio.ac.jp>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>
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On Mon, 26 Apr 2021 at 11:19, Kenta Ishiguro
<kentaishiguro@sslab.ics.keio.ac.jp> wrote:
>
> Thank you for the reply.
>
> My question is about following scenario:
> 1. running vCPU receives IPI and the vCPU's ipi_received gets true
> 2. the vCPU responds to the IPI
> 3. the vCPU exits
> 4. the vCPU is preempted by KVM
> 5. the vCPU is boosted, but it has already responded to the IPI
> 6. the vCPU enters and the vCPU's ipi_received is cleaned
>
> In this case, I think the check of vcpu->preempted does not limit the candidate vCPUs.

Good point, you are right. However, actually I played with that code a
bit before, I have another version adding the vcpu->preempted checking
when marking IPI receiver, the score is not as good as expected.

    Wanpeng