From: Peter Zijlstra <peterz@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
"Durrant, Paul" <pdurrant@amazon.co.uk>,
"Allister, Jack" <jalliste@amazon.com>,
"bp@alien8.de" <bp@alien8.de>,
"diapop@amazon.co.uk" <diapop@amazon.co.uk>,
"hpa@zytor.com" <hpa@zytor.com>,
"jmattson@google.com" <jmattson@google.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"metikaya@amazon.co.uk" <metikaya@amazon.co.uk>,
"mingo@redhat.com" <mingo@redhat.com>,
"rkrcmar@redhat.com" <rkrcmar@redhat.com>,
"sean.j.christopherson@intel.com"
<sean.j.christopherson@intel.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"wanpengli@tencent.com" <wanpengli@tencent.com>,
"x86@kernel.org" <x86@kernel.org>
Subject: Re: ...\n
Date: Wed, 1 Jun 2022 12:19:07 +0200 [thread overview]
Message-ID: <Ypc9G3nTkib1y9X4@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <b9238c07-68a7-31fa-c654-d8111a1e2d4b@redhat.com>
On Wed, Jun 01, 2022 at 10:59:17AM +0200, Paolo Bonzini wrote:
> On 6/1/22 09:57, Vitaly Kuznetsov wrote:
> > > > 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.
>
> True, but then there's also a policy issue, in that KVM shouldn't be allowed
> to *bump* the frequency if userspace would ordinarily not have access to the
> cpufreq files in sysfs.
So, when using schedutil (which requires intel_pstate in passive mode),
then there's the option to use per-task uclamps which are somewhat
complicated but also affect cpufreq.
next prev parent reply other threads:[~2022-06-01 10:19 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-31 10:59 [PATCH] KVM: VMX: CPU frequency scaling for intel x86_64 KVM guests Jack Allister
2022-05-31 11:43 ` Metin Kaya
2022-05-31 18:11 ` Paolo Bonzini
2022-06-01 12:55 ` David Woodhouse
2022-05-31 13:38 ` Peter Zijlstra
2022-05-31 14:02 ` ...\n Jack Allister
2022-05-31 14:44 ` ...\n Peter Zijlstra
2022-05-31 14:52 ` ...\n Durrant, Paul
2022-05-31 15:51 ` ...\n Paolo Bonzini
2022-06-01 7:57 ` ...\n Vitaly Kuznetsov
2022-06-01 8:59 ` ...\n Paolo Bonzini
2022-06-01 10:19 ` Peter Zijlstra [this message]
2022-06-01 6:52 ` ...\n Peter Zijlstra
2022-06-01 8:03 ` ...\n Vitaly Kuznetsov
2022-06-01 8:25 ` ...\n Christophe de Dinechin
2022-06-01 8:54 ` ...\n Durrant, Paul
2022-06-01 8:57 ` ...\n Paolo Bonzini
2022-06-01 9:20 ` ...\n Durrant, Paul
2022-06-01 9:43 ` ...\n Amit Shah
2022-06-01 13:14 ` ...\n David Woodhouse
2022-05-31 14:52 ` ...\n Paolo Bonzini
2022-05-31 15:27 ` ...\n Peter Zijlstra
2022-05-31 15:01 ` [PATCH] KVM: VMX: CPU frequency scaling for intel x86_64 KVM guests Vitaly Kuznetsov
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