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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id a4-20020a1709065f8400b006f3ef214dfesm390234eju.100.2022.06.01.00.57.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jun 2022 00:57:15 -0700 (PDT) From: Vitaly Kuznetsov To: Paolo Bonzini , "Durrant, Paul" , Peter Zijlstra , "Allister, Jack" 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" , "rkrcmar@redhat.com" , "sean.j.christopherson@intel.com" , "tglx@linutronix.de" , "wanpengli@tencent.com" , "x86@kernel.org" Subject: Re: ...\n In-Reply-To: <307f19cc-322e-c900-2894-22bdee1e248a@redhat.com> References: <20220531140236.1435-1-jalliste@amazon.com> <059ab3327ac440479ecfdf49fa054347@EX13D32EUC003.ant.amazon.com> <307f19cc-322e-c900-2894-22bdee1e248a@redhat.com> Date: Wed, 01 Jun 2022 09:57:14 +0200 Message-ID: <87tu94olyd.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 5/31/22 16:52, Durrant, Paul wrote: >>> -----Original Message----- >>> From: Peter Zijlstra >>> Sent: 31 May 2022 15:44 >>> To: Allister, Jack >>> 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