linux-kernel - Re: [PATCH] perf pmu: Consider raw events as legacy events

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Message-ID: <CAP-5=fVvth_HnfnPNxtHe=FzxT9hNNKKDLGCSvQfLqwTY4WpHg@mail.gmail.com>
Date: Wed, 7 May 2025 08:42:27 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Kan Liang <kan.liang@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf pmu: Consider raw events as legacy events

On Tue, May 6, 2025 at 3:23 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> When it finds a matching pmu for a legacy event, it should look for
> core pmus.  The raw events also refers to core events so it should be
> handled together.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/pmus.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> index b99292de76693dbb..0134321fc520b1fc 100644
> --- a/tools/perf/util/pmus.c
> +++ b/tools/perf/util/pmus.c
> @@ -726,7 +726,8 @@ struct perf_pmu *evsel__find_pmu(const struct evsel *evsel)
>         pmu = perf_pmus__find_by_type(evsel->core.attr.type);
>         legacy_core_type =
>                 evsel->core.attr.type == PERF_TYPE_HARDWARE ||
> -               evsel->core.attr.type == PERF_TYPE_HW_CACHE;
> +               evsel->core.attr.type == PERF_TYPE_HW_CACHE ||
> +               evsel->core.attr.type == PERF_TYPE_RAW;

I don't think this is right. The PERF_TYPE_RAW isn't a legacy type as
we map sysfs/json names to the format encoding. More than this, the
extended type information will not be present for a raw type and so
this change could cause an invalid PMU to be looked up on
hybrid/BIG.little systems. On x86 the cpu or cpu_core PMU will have
type PERF_TYPE_RAW (4). As is common ARM decided to do things
differently, meaning there is no type 4 to a PMU mapping. I think we
need a change like:
```
diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index b99292de7669..6632209c6664 100644
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -727,14 +727,21 @@ struct perf_pmu *evsel__find_pmu(const struct
evsel *evsel)
       legacy_core_type =
               evsel->core.attr.type == PERF_TYPE_HARDWARE ||
               evsel->core.attr.type == PERF_TYPE_HW_CACHE;
-       if (!pmu && legacy_core_type) {
-               if (perf_pmus__supports_extended_type()) {
-                       u32 type = evsel->core.attr.config >>
PERF_PMU_TYPE_SHIFT;
+       if (!pmu && legacy_core_type && perf_pmus__supports_extended_type()) {
+               u32 type = evsel->core.attr.config >> PERF_PMU_TYPE_SHIFT;

-                       pmu = perf_pmus__find_by_type(type);
-               } else {
-                       pmu = perf_pmus__find_core_pmu();
-               }
+               pmu = perf_pmus__find_by_type(type);
+       }
+       if (!pmu && (legacy_core_type || evsel->core.attr.type ==
PERF_TYPE_RAW)) {
+               /*
+                * For legacy events, if there was no extended type info then
+                * assume the PMU is the first core PMU.
+                *
+                * On architectures like ARM there is no sysfs PMU with type
+                * PERF_TYPE_RAW, assume the RAW events are going to be handled
+                * by the first core PMU.
+                */
+               pmu = perf_pmus__find_core_pmu();
       }
       ((struct evsel *)evsel)->pmu = pmu;
       return pmu;
```
which handles both the case that the extended type was missing on
hybrid/BIG.little and the ARM raw type problem.

Thanks,
Ian

>         if (!pmu && legacy_core_type) {
>                 if (perf_pmus__supports_extended_type()) {
>                         u32 type = evsel->core.attr.config >> PERF_PMU_TYPE_SHIFT;
> --
> 2.49.0.987.g0cc8ee98dc-goog
>