Messages in this thread | | | Date | Mon, 2 Oct 2023 15:30:07 +0200 | From | Ingo Molnar <> | Subject | Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics event |
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* Peter Zijlstra <peterz@infradead.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
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