linux-kernel - Re: [PATCH v2] perf metrics: Add literal for system TSC frequency

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Message-ID: <YpJCUM08I6mRkho/@hirez.programming.kicks-ass.net>
Date:   Sat, 28 May 2022 17:40:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Andi Kleen <ak@...ux.intel.com>, perry.taylor@...el.com,
        caleb.biggers@...el.com, kshipra.bopardikar@...el.com,
        Kan Liang <kan.liang@...ux.intel.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        James Clark <james.clark@....com>,
        John Garry <john.garry@...wei.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] perf metrics: Add literal for system TSC frequency

On Sat, May 28, 2022 at 07:50:40AM -0700, Ian Rogers wrote:
> On Sat, May 28, 2022 at 7:02 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Fri, May 27, 2022 at 07:54:19AM -0700, Andi Kleen wrote:
> >
> > > > This all seems bonghits inspired... and perf actually does expose the
> > > > tsc frequency. What do you think is in perf_event_mmap_page::time_* ?
> > >
> > >
> > > That's not really available to perf stat, which is the primary metrics user.
> >
> > Why not? You can mmap any perf-fd (even software events) and these
> > fields should be filled out.
> >
> > It should work on any x86 CPU that has a TSC. The only caveat is that
> > the kernel must not have marked the TSC unstable.
> >
> > It could even work for virt -- all you need is for virt to use
> > native_sched_clock() instead of the paravirt nonsense.
> 
> It will at least fail if inherit is enabled, no?

For per-task events, yes, I suppose it will. I'd forgotten about that
restriction on perf_mmap() :/