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

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Date:   Sat, 28 May 2022 07:50:40 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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?

Thanks,
Ian