linux-kernel - Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers

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Message-ID: <f3c2cc31-6388-f7b5-48fd-fb19d059eea3@redhat.com>
Date:   Mon, 27 Apr 2020 21:10:26 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>,
        "Li,Rongqing" <lirongqing@...du.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers

On 27/04/20 19:30, Jim Mattson wrote:
>>>> I would like to see performance data before enabling this
>>>> unconditionally.
>>> I wouldn't want this to be enabled unconditionally anyway,
>>> because you need to take into account live migration to and from
>>> processors that do not have APERF/MPERF support.
>>> 
>>> Paolo
>> I will add a kvm parameter to consider whether enable MPERF/APERF
>> emulations, and make default value to false
>
> Wouldn't it be better to add a per-VM capability to enable this
> feature?

Yes, you it would be better to use KVM_ENABLE_CAP indeed.

Paolo