linux-kernel - Re: ...\n

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Message-ID: <YpYz+ltAHRsF5s0u@hirez.programming.kicks-ass.net>
Date:   Tue, 31 May 2022 17:27:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jack Allister <jalliste@...zon.com>,
        Borislav Petkov <bp@...en8.de>, diapop@...zon.co.uk,
        "Anvin, H. Peter" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        "Kernel Mailing List, Linux" <linux-kernel@...r.kernel.org>,
        Metin Kaya <metikaya@...zon.co.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: ...\n

On Tue, May 31, 2022 at 04:52:56PM +0200, Paolo Bonzini wrote:
> On Tue, May 31, 2022 at 4:45 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > 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.
> 
> It is a weird usecase indeed, but actually it *is* enforced by the
> host in Jack's patch.

Clearly I don't understand KVM much; I was thikning that since it was
mucking the with vmx code it was some guest interface.

If it is host control, then it's even more insane, since the host has
plenty existing interfaces for cpufreq control. No need to add more
crazy hacks like this.