linux-kernel - Re: [RFC PATCH 0/2] Mitigating Excessive Pause-Loop Exiting in VM-Agnostic KVM

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Date:   Wed, 21 Apr 2021 16:19:36 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kenta Ishiguro <kentaishiguro@...ab.ics.keio.ac.jp>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pl@...ab.ics.keio.ac.jp,
        kono@...ab.ics.keio.ac.jp
Subject: Re: [RFC PATCH 0/2] Mitigating Excessive Pause-Loop Exiting in
 VM-Agnostic KVM

On Thu, Apr 22, 2021, Kenta Ishiguro wrote:
> To solve problems (2) and (3), patch 2 monitors IPI communication between
> vCPUs and leverages the relationship between vCPUs to select boost
> candidates.  The "[PATCH] KVM: Boost vCPU candidiate in user mode which is
> delivering interrupt" patch
> (https://lore.kernel.org/kvm/CANRm+Cy-78UnrkX8nh5WdHut2WW5NU=UL84FRJnUNjsAPK+Uww@mail.gmail.com/T/)
> seems to be effective for (2) while it only uses the IPI receiver
> information.

On the IPI side of thing, I like the idea of explicitly tracking the IPIs,
especially if we can simplify the implementation, e.g. by losing the receiver
info and making ipi_received a bool.  Maybe temporarily table Wanpeng's patch
while this approach is analyzed?