linux-kernel - Re: ...\n

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Message-ID: <87tu94olyd.fsf@redhat.com>
Date:   Wed, 01 Jun 2022 09:57:14 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "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>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: ...\n

Paolo Bonzini <pbonzini@...hat.com> writes:

> 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.

KVM may probably use the cpufreq API to run each vCPU at the desired
frequency: I don't quite see how this can be done with a VMM today when
it's not a 1-vCPU-per-1-pCPU setup.

-- 
Vitaly