linux-kernel - Re: [PATCH v1 02/20] perf jevents: Add idle metric for Intel models

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Date: Fri, 1 Mar 2024 09:49:54 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Perry Taylor <perry.taylor@...el.com>,
	Samantha Alt <samantha.alt@...el.com>,
	Caleb Biggers <caleb.biggers@...el.com>,
	Weilin Wang <weilin.wang@...el.com>,
	Edward Baker <edward.baker@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	John Garry <john.g.garry@...cle.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Jing Zhang <renyu.zj@...ux.alibaba.com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	James Clark <james.clark@....com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v1 02/20] perf jevents: Add idle metric for Intel models

> +def Idle() -> Metric:
> +  cyc = Event("msr/mperf/")
> +  tsc = Event("msr/tsc/")
> +  low = max(tsc - cyc, 0)
> +  return Metric(
> +      "idle",
> +      "Percentage of total wallclock cycles where CPUs are in low power state (C1 or deeper sleep state)",
> +      d_ratio(low, tsc), "100%")

TBH I fail to see the advantage over the JSON. That's much more verbose
and we don't expect to have really complex metrics anyways.

And then we have a gigantic patch kit for what gain?

The motivation was the lack of comments in JSON? We could just add some
to the parser (e.g. with /* */ ).  And we could allow an JSON array for the
expression to get multiple lines.


-Andi