Re: ...\n

[Vitaly Kuznetsov]

Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:

> On 5/31/22 16:52, Durrant, Paul wrote:
>>> -----Original Message-----
>>> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>>> Sent: 31 May 2022 15:44
>>> To: Allister, Jack <jalliste@xxxxxxxxxx>
>>> Cc: bp@xxxxxxxxx; diapop@xxxxxxxxxxxx; hpa@xxxxxxxxx; jmattson@xxxxxxxxxx; joro@xxxxxxxxxx;
>>> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; metikaya@xxxxxxxxxxxx; mingo@xxxxxxxxxx;
>>> pbonzini@xxxxxxxxxx; rkrcmar@xxxxxxxxxx; sean.j.christopherson@xxxxxxxxx; tglx@xxxxxxxxxxxxx;
>>> vkuznets@xxxxxxxxxx; wanpengli@xxxxxxxxxxx; x86@xxxxxxxxxx
>>> 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