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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id j4-20020a508a84000000b0042aa153e73esm8802086edj.12.2022.05.31.08.51.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 May 2022 08:51:50 -0700 (PDT) Message-ID: <307f19cc-322e-c900-2894-22bdee1e248a@redhat.com> Date: Tue, 31 May 2022 17:51:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: ...\n Content-Language: en-US To: "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" , "vkuznets@redhat.com" , "wanpengli@tencent.com" , "x86@kernel.org" References: <20220531140236.1435-1-jalliste@amazon.com> <059ab3327ac440479ecfdf49fa054347@EX13D32EUC003.ant.amazon.com> From: Paolo Bonzini In-Reply-To: <059ab3327ac440479ecfdf49fa054347@EX13D32EUC003.ant.amazon.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Paolo