linux-kernel - Re: [PATCH v2 00/12] CPU mask improvements/fixes particularly for hybrid

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Message-ID: <aHqQQwI0MckHdBlY@google.com>
Date: Fri, 18 Jul 2025 11:19:47 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Thomas Falcon <thomas.falcon@...el.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@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Ben Gainey <ben.gainey@....com>,
	James Clark <james.clark@...aro.org>,
	Howard Chu <howardchu95@...il.com>,
	Weilin Wang <weilin.wang@...el.com>, Levi Yun <yeoreum.yun@....com>,
	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Zhongqiu Han <quic_zhonhan@...cinc.com>,
	Blake Jones <blakejones@...gle.com>,
	Yicong Yang <yangyicong@...ilicon.com>,
	Anubhav Shelat <ashelat@...hat.com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	Jean-Philippe Romain <jean-philippe.romain@...s.st.com>,
	Song Liu <song@...nel.org>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/12] CPU mask improvements/fixes particularly for
 hybrid

On Thu, Jul 17, 2025 at 02:02:21PM -0700, Ian Rogers wrote:
> On hybrid systems some PMUs apply to all core types, particularly for
> metrics the msr PMU and the tsc event. The metrics often only want the
> values of the counter for their specific core type. These patches
> allow the cpu term in an event to give a PMU name to take the cpumask
> from. For example:
> 
>   $ perf stat -e msr/tsc,cpu=cpu_atom/ ...
> 
> will aggregate the msr/tsc/ value but only for atom cores. In doing
> this problems were identified in how cpumasks are handled by parsing
> and event setup when cpumasks are specified along with a task to
> profile. The event parsing, cpumask evlist propagation code and perf
> stat code are updated accordingly.
> 
> The final result of the patch series is to be able to run:
> ```
> $ perf stat --no-scale -e 'msr/tsc/,msr/tsc,cpu=cpu_core/,msr/tsc,cpu=cpu_atom/' perf test -F 10
>  10.1: Basic parsing test                                            : Ok
>  10.2: Parsing without PMU name                                      : Ok
>  10.3: Parsing with PMU name                                         : Ok
> 
>  Performance counter stats for 'perf test -F 10':
> 
>         63,704,975      msr/tsc/
>         47,060,704      msr/tsc,cpu=cpu_core/                        (4.62%)
>         16,640,591      msr/tsc,cpu=cpu_atom/                        (2.18%)
> ```
> 
> This has (further) identified a kernel bug for task events around the
> enabled time being too large leading to invalid scaling (hence the
>  --no-scale in the command line above).
> 
> v2: Add additional documentation of the cpu term to `perf list`
>     (Namhyung), extend the term to also allow CPU ranges. Add Thomas
>     Falcon's reviewed-by. Still open for discussion whether the term
>     cpu should have >1 variant for PMUs, etc. or whether the single
>     term is okay. We could refactor later and add a term, but that
>     would break existing users, but they are most likely to be metrics
>     so probably not a huge issue.

I slightly prefer a new term to minimize the possible confusion.  But
it's not strong and I'm open to other opinion.

On the other hand, the 'cpu' term is new and I don't think it has many
users outside.  So probably we can change it later.

Thanks,
Namhyung

> 
> Ian Rogers (12):
>   perf parse-events: Warn if a cpu term is unsupported by a CPU
>   perf stat: Avoid buffer overflow to the aggregation map
>   perf stat: Don't size aggregation ids from user_requested_cpus
>   perf parse-events: Allow the cpu term to be a PMU or CPU range
>   perf tool_pmu: Allow num_cpus(_online) to be specific to a cpumask
>   libperf evsel: Rename own_cpus to pmu_cpus
>   libperf evsel: Factor perf_evsel__exit out of perf_evsel__delete
>   perf evsel: Use libperf perf_evsel__exit
>   perf pmus: Factor perf_pmus__find_by_attr out of evsel__find_pmu
>   perf parse-events: Minor __add_event refactoring
>   perf evsel: Add evsel__open_per_cpu_and_thread
>   perf parse-events: Support user CPUs mixed with threads/processes
> 
>  tools/lib/perf/evlist.c                 | 118 ++++++++++++++++--------
>  tools/lib/perf/evsel.c                  |   9 +-
>  tools/lib/perf/include/internal/evsel.h |   3 +-
>  tools/perf/Documentation/perf-list.txt  |  25 +++--
>  tools/perf/builtin-stat.c               |   9 +-
>  tools/perf/tests/event_update.c         |   4 +-
>  tools/perf/util/evlist.c                |  15 +--
>  tools/perf/util/evsel.c                 |  55 +++++++++--
>  tools/perf/util/evsel.h                 |   5 +
>  tools/perf/util/expr.c                  |   2 +-
>  tools/perf/util/header.c                |   4 +-
>  tools/perf/util/parse-events.c          | 112 ++++++++++++++++------
>  tools/perf/util/pmus.c                  |  29 +++---
>  tools/perf/util/pmus.h                  |   2 +
>  tools/perf/util/stat.c                  |   6 +-
>  tools/perf/util/synthetic-events.c      |   4 +-
>  tools/perf/util/tool_pmu.c              |  56 +++++++++--
>  tools/perf/util/tool_pmu.h              |   2 +-
>  18 files changed, 323 insertions(+), 137 deletions(-)
> 
> -- 
> 2.50.0.727.gbf7dc18ff4-goog
>