Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        "Durrant, Paul" <pdurrant@amazon.co.uk>
Cc:     "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>,
        "pbonzini@redhat.com" <pbonzini@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
In-Reply-To: <YpcMw2TgNWzrcoRm@worktop.programming.kicks-ass.net>
References: <YpYaYK7a28DFT5Ne@hirez.programming.kicks-ass.net>
 <20220531140236.1435-1-jalliste@amazon.com>
 <YpYpxzt4rmG+LFy9@hirez.programming.kicks-ass.net>
 <059ab3327ac440479ecfdf49fa054347@EX13D32EUC003.ant.amazon.com>
 <YpcMw2TgNWzrcoRm@worktop.programming.kicks-ass.net>
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

Peter Zijlstra <peterz@infradead.org> 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