linux-kernel - Re: ...\n

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Message-ID: <307f19cc-322e-c900-2894-22bdee1e248a@redhat.com>
Date:   Tue, 31 May 2022 17:51:47 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Durrant, Paul" <pdurrant@...zon.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        "Allister, Jack" <jalliste@...zon.com>
Cc:     "bp@...en8.de" <bp@...en8.de>,
        "diapop@...zon.co.uk" <diapop@...zon.co.uk>,
        "hpa@...or.com" <hpa@...or.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "metikaya@...zon.co.uk" <metikaya@...zon.co.uk>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: ...\n

On 5/31/22 16:52, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Peter Zijlstra <peterz@...radead.org>
>> Sent: 31 May 2022 15:44
>> To: Allister, Jack <jalliste@...zon.com>
>> Cc: bp@...en8.de; diapop@...zon.co.uk; hpa@...or.com; jmattson@...gle.com; joro@...tes.org;
>> kvm@...r.kernel.org; linux-kernel@...r.kernel.org; metikaya@...zon.co.uk; mingo@...hat.com;
>> pbonzini@...hat.com; rkrcmar@...hat.com; sean.j.christopherson@...el.com; tglx@...utronix.de;
>> vkuznets@...hat.com; wanpengli@...cent.com; x86@...nel.org
>> Subject: RE: [EXTERNAL]...\n
>>
>>
>> On Tue, May 31, 2022 at 02:02:36PM +0000, Jack Allister wrote:
>>> The reasoning behind this is that you may want to run a guest at a
>>> lower CPU frequency for the purposes of trying to match performance
>>> parity between a host of an older CPU type to a newer faster one.
>>
>> That's quite ludicrus. Also, then it should be the host enforcing the
>> cpufreq, not the guest.
> 
> I'll bite... What's ludicrous about wanting to run a guest at a lower CPU freq to minimize observable change in whatever workload it is running?

Well, the right API is cpufreq, there's no need to make it a KVM 
functionality.

Paolo