linux-kernel - Re: [PATCH v4 0/3] Add arch TSC frequency information

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Message-ID: <6dfdeeee-1c28-666d-1385-c4bcc493cc6a@linux.intel.com>
Date:   Mon, 18 Jul 2022 13:26:22 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Ian Rogers <irogers@...gle.com>, perry.taylor@...el.com,
        caleb.biggers@...el.com, kshipra.bopardikar@...el.com,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        Andi Kleen <ak@...ux.intel.com>,
        James Clark <james.clark@....com>,
        John Garry <john.garry@...wei.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v4 0/3] Add arch TSC frequency information



On 2022-07-18 12:43 p.m., Ian Rogers wrote:
> The first patch adds the #system_tsc_freq literal to expr.c and
> computes it via cpuid. The second patches adds support for "older"
> processors by computing the value via /proc/cpuinfo. The third patch
> adds a test then the computation looks somewhat sensible.
> 
> Such a literal is useful to calculate things like the average
> frequency [1]. The TSC frequency isn't exposed by sysfs although some
> experimental drivers look to add it [2].
> 
> [1] https://github.com/intel/perfmon-metrics/blob/5ad9ef7056f31075e8178b9f1fb732af183b2c8d/SKX/metrics/perf/skx_metric_perf.json#L11
> [2] https://github.com/trailofbits/tsc_freq_khz
> 
> v4. Modified the patch order and separated out the test.
> v3. Added the cpuid approach from Kan Liang.
> v2. Adds warnings to make clear if things have changed/broken on future
>     Intel platforms. It also adds caching and an Intel specific that a
>     value is computed.
> 
> Ian Rogers (2):
>   perf tsc: Add cpuinfo fall back for arch_get_tsc_freq
>   perf test: Add test for #system_tsc_freq in metrics

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan

> 
> Kan Liang (1):
>   perf tsc: Add arch TSC frequency information
> 
>  tools/perf/arch/x86/util/cpuid.h  | 34 ++++++++++++++
>  tools/perf/arch/x86/util/header.c | 27 +++++------
>  tools/perf/arch/x86/util/tsc.c    | 77 +++++++++++++++++++++++++++++++
>  tools/perf/tests/expr.c           | 13 ++++++
>  tools/perf/util/expr.c            | 13 ++++++
>  tools/perf/util/tsc.h             |  1 +
>  6 files changed, 149 insertions(+), 16 deletions(-)
>  create mode 100644 tools/perf/arch/x86/util/cpuid.h
>