Re: ...\n

Vitaly Kuznetsov
2022-06-01T07:57:26Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 5/31/22 16:52, Durrant, Paul wrote:
>>> -----Original Message-----
>>> From: Peter Zijlstra <peterz@infradead.org>
>>> Sent: 31 May 2022 15:44
>>> To: Allister, Jack <jalliste@amazon.com>
>>> Cc: bp@alien8.de; diapop@amazon.co.uk; hpa@zytor.com; jmattson@google.com; joro@8bytes.org;
>>> kvm@vger.kernel.org; linux-kernel@vger.kernel.org; metikaya@amazon.co.uk; mingo@redhat.com;
>>> pbonzini@redhat.com; rkrcmar@redhat.com; sean.j.christopherson@intel.com; tglx@linutronix.de;
>>> vkuznets@redhat.com; wanpengli@tencent.com; x86@kernel.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