linux-kernel - Re: [PATCH 0/2] KVM: x86: Fix incorrect VM-exit profiling

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Message-ID: <CAN86XOYNpzEUN0aL9g=_GQFz5zdXX9Pvcs_TDmBVyJZDTfXREg@mail.gmail.com>
Date:   Wed, 11 May 2022 18:45:00 +0200
From:   Wei Zhang <zhanwei@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Suleiman Souhlal <suleiman@...gle.com>,
        Sangwhan Moon <sxm@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        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>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] KVM: x86: Fix incorrect VM-exit profiling

Yes, the profiling is about finding out which instructions in the
guest trigger VM exits and the corresponding frequencies.

Basically this will give a histogram array in /proc/profile. So if
'array[A] == T', we know that the instruction at (_stext + A) triggers
VM exits T times. readprofile command could read the information and
show a summary.




On Tue, May 10, 2022 at 1:57 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Tue, Apr 12, 2022, Wei Zhang wrote:
> > The profile=kvm boot option has been useful because it provides a
> > convenient approach to profile VM exits.
>
> What exactly are you profiling?  Where the guest executing at any given exit?  Mostly
> out of curiosity, but also in the hope that we might be able to replace profiling with
> a dedicated KVM stat(s).