[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZRrF38RGllA04R8o@gmail.com>
Date: Mon, 2 Oct 2023 15:30:07 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Sean Christopherson <seanjc@...gle.com>,
Dapeng Mi <dapeng1.mi@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Kan Liang <kan.liang@...ux.intel.com>,
Like Xu <likexu@...cent.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>, kvm@...r.kernel.org,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
Zhenyu Wang <zhenyuw@...ux.intel.com>,
Zhang Xiong <xiong.y.zhang@...el.com>,
Lv Zhiyuan <zhiyuan.lv@...el.com>,
Yang Weijiang <weijiang.yang@...el.com>,
Dapeng Mi <dapeng1.mi@...el.com>,
Jim Mattson <jmattson@...gle.com>,
David Dunn <daviddunn@...gle.com>,
Mingwei Zhang <mizhang@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics
event
* Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Sep 29, 2023 at 03:46:55PM +0000, Sean Christopherson wrote:
>
> > > I will firmly reject anything that takes the PMU away from the host
> > > entirely through.
> >
> > Why? What is so wrong with supporting use cases where the platform owner *wants*
> > to give up host PMU and NMI watchdog functionality? If disabling host PMU usage
> > were complex, highly invasive, and/or difficult to maintain, then I can understand
> > the pushback.
>
> Because it sucks.
>
> You're forcing people to choose between no host PMU or a slow guest PMU.
> And that's simply not a sane choice for most people -- worse it's not a
> choice based in technical reality.
>
> It's a choice out of lazyness, disabling host PMU is not a requirement
> for pass-through.
Not just a choice of laziness, but it will clearly be forced upon users
by external entities:
"Pass ownership of the PMU to the guest and have no host PMU, or you
won't have sane guest PMU support at all. If you disagree, please open
a support ticket, which we'll ignore."
The host OS shouldn't offer facilities that severely limit its own capabilities,
when there's a better solution. We don't give the FPU to apps exclusively either,
it would be insanely stupid for a platform to do that.
Thanks,
Ingo
Powered by blists - more mailing lists