From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 295ACC433EF for ; Wed, 1 Jun 2022 08:03:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350489AbiFAIDQ (ORCPT ); Wed, 1 Jun 2022 04:03:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40158 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350006AbiFAIDO (ORCPT ); Wed, 1 Jun 2022 04:03:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2392545AD5 for ; Wed, 1 Jun 2022 01:03:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1654070590; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Xgdti+VwJR3VZPhJkWljxyzD9ChCNJZ2LKlv/SAahT4=; b=Lzp63RcJB7AoHProNPwvNLJWzBO74jRLI6WAGPYqIAKRxqOccR0z74pjG+NXfrZhekIbtS xmijPBpLkxb8lUHNIGR03R44BJVr4EBjuy0x+VjS5LFMz1Nb/SPmPYTFT8vp5rsQF5EXkV ZNDkTO69loqX7z5VMhJW5g6hUk2f04Y= Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-32-aKxRQNR8MCOdvzRMeYr2AA-1; Wed, 01 Jun 2022 04:03:09 -0400 X-MC-Unique: aKxRQNR8MCOdvzRMeYr2AA-1 Received: by mail-ed1-f71.google.com with SMTP id y13-20020a056402358d00b0042dfb820070so446350edc.6 for ; Wed, 01 Jun 2022 01:03:09 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=Xgdti+VwJR3VZPhJkWljxyzD9ChCNJZ2LKlv/SAahT4=; b=3cuWmGAFOfxa/BIGAb2kci2mO2wKWrXLepOpminFc53V+TEQ0tkHTF61Hp7BTx5KXy aKoLoDy0GLHuadklp7hxx9Wh4/PRu5MmuCWvjEyHpx4bfDQeCqwKxDkrtDGSkolBwUwu LtoKrT2e4D66yU6bJMvS9OdyNJJ1lxkg1KBIxPzaACw5FhoDax561ImJ7325rBSWW8vr uAurlotcLiJ0b8ZRUXTg938Y+iI3EVKzSjRw7pGqwpYYUViEoz25hccCaMCoHitDs66P /AuCJrpZdDUE5PQ8PiJGs3qAknYKGhzZ8c3ljIOGDWUrn9IsqSpbnoCgc1BqLSbq1nw7 H47g== X-Gm-Message-State: AOAM532VXwgaWFJLJCpis4RGSFPYw1nLzj/rBndc10T0vepqltQhiQ7E P/Dw/nB4Y2E5rLSvvqvMOQVrBjXa0jwSorxvVXBW2l+nh3ghvFQee1q9e9pxhQ1EL5+751X96Zn NDoPK4w5XOYYI X-Received: by 2002:a05:6402:34c1:b0:42b:4047:20b8 with SMTP id w1-20020a05640234c100b0042b404720b8mr57064182edc.88.1654070588084; Wed, 01 Jun 2022 01:03:08 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwgO9mu44S3VLlU3/wD7qn0U/ff1HsZNyCf5jYGov3NDArM7pwpMiurcfJY5MoE5bqD3r/3EA== X-Received: by 2002:a05:6402:34c1:b0:42b:4047:20b8 with SMTP id w1-20020a05640234c100b0042b404720b8mr57064153edc.88.1654070587868; Wed, 01 Jun 2022 01:03:07 -0700 (PDT) Received: from fedora (nat-2.ign.cz. [91.219.240.2]) by smtp.gmail.com with ESMTPSA id wj17-20020a170907051100b006fed9a0eb17sm388609ejb.187.2022.06.01.01.03.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jun 2022 01:03:07 -0700 (PDT) From: Vitaly Kuznetsov To: Peter Zijlstra , "Durrant, Paul" Cc: "Allister, Jack" , "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" , "wanpengli@tencent.com" , "x86@kernel.org" Subject: Re: ...\n In-Reply-To: References: <20220531140236.1435-1-jalliste@amazon.com> <059ab3327ac440479ecfdf49fa054347@EX13D32EUC003.ant.amazon.com> Date: Wed, 01 Jun 2022 10:03:06 +0200 Message-ID: <87r148olol.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Peter Zijlstra writes: > On Tue, May 31, 2022 at 02:52:04PM +0000, Durrant, Paul 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? > > *why* would you want to do that? Everybody wants their stuff done > faster. > FWIW, I can see a valid use-case: imagine you're running some software which calibrates itself in the beginning to run at some desired real time speed but then the VM running it has to be migrated to a host with faster (newer) CPUs. I don't have a real world examples out of top of my head but I remember some old DOS era games were impossible to play on newer CPUs because everything was happenning too fast. Maybe that's the case :-) -- Vitaly