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From: Ian Rogers <irogers@google.com>
Date: Wed, 3 Apr 2024 13:23:51 -0700
Message-ID: <CAP-5=fU1ZC2dAr-U9kecXxxVAyyx3BtnQVOAax2PtvzEfAKjyg@mail.gmail.com>
Subject: Re: [PATCH v1] perf metrics: Remove the "No_group" metric group
To: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, Namhyung Kim <namhyung@kernel.org>, 
	Mark Rutland <mark.rutland@arm.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Adrian Hunter <adrian.hunter@intel.com>, Kan Liang <kan.liang@linux.intel.com>, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
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On Wed, Apr 3, 2024 at 11:44=E2=80=AFAM Andi Kleen <ak@linux.intel.com> wro=
te:
>
> On Wed, Apr 03, 2024 at 09:46:36AM -0700, Ian Rogers wrote:
> > Rather than place metrics without a metric group in "No_group" place
> > them in a a metric group that is their name. Still allow such metrics
> > to be selected if "No_group" is passed, this change just impacts perf
> > list.
>
> But what's the point of it? It will just make perf list more verbose,
> but I don't see any advantage.

So it is possible to list all metrics, that's not changed here. The
thing I'm looking to change is that when a metric is standalone it
appears in "perf list metricgroups". The reason is that a metric group
can gather a bunch of related metrics, say some form of read, write
and total bandwidth, whereas something like an idle metric
("d_ratio(max(msr@tsc@ - msr@mperf@, 0), msr@tsc@)") that could get
placed in No_group is more useful if it appears in a metric group of
"idle". I'd put forward that nobody ever wants to run "idle" as part
of "No_group" whereas being able to see it as a thing in metricgroups
is useful. I want to be able to run "perf list metricgroups" and get
groups of 1 or more metrics that someone might want to pass to "perf
stat -M", currently this just shows when there is a group of more than
1 metric as there is no practice of putting a metric like "idle" into
a metric group called "idle". We could update all metrics to make it
so that when they don't have a metric group we add them to one with
their name. We could do this in jevents.py. Those changes would make
the No_group logic redundant, so we should remove it. Just updating
the No_group logic in the perf command seemed like the minimal
approach.

Thanks,
Ian

> -Andi