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Date: Mon, 7 Mar 2022 15:42:07 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Adrian Hunter <adrian.hunter@...el.com> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, kvm@...r.kernel.org, H Peter Anvin <hpa@...or.com>, Mathieu Poirier <mathieu.poirier@...aro.org>, Suzuki K Poulose <suzuki.poulose@....com>, Leo Yan <leo.yan@...aro.org>, jgross@...e.com, sdeep@...are.com, pv-drivers@...are.com, pbonzini@...hat.com, seanjc@...gle.com, kys@...rosoft.com, sthemmin@...rosoft.com, virtualization@...ts.linux-foundation.org, Andrew.Cooper3@...rix.com, christopher.s.hall@...el.com Subject: Re: [PATCH V2 03/11] perf/x86: Add support for TSC in nanoseconds as a perf event clock On Mon, Mar 07, 2022 at 02:36:03PM +0200, Adrian Hunter wrote: > > diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c > > index 4420499f7bb4..a1f179ed39bf 100644 > > --- a/arch/x86/kernel/paravirt.c > > +++ b/arch/x86/kernel/paravirt.c > > @@ -145,6 +145,15 @@ DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock); > > > > void paravirt_set_sched_clock(u64 (*func)(void)) > > { > > + /* > > + * Anything with ART on promises to have sane TSC, otherwise the whole > > + * ART thing is useless. In order to make ART useful for guests, we > > + * should continue to use the TSC. As such, ignore any paravirt > > + * muckery. > > + */ > > + if (cpu_feature_enabled(X86_FEATURE_ART)) > > Does not seem to work because the feature X86_FEATURE_ART does not seem to get set. > Possibly because detect_art() excludes anything running on a hypervisor. Simple enough to delete that clause I suppose. Christopher, what is needed to make that go away? I suppose the guest needs to be aware of the active TSC scaling parameters to make it work ?
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