linux-kernel - Re: [PATCH v1] perf stat: Additional verbose details for <not supported> events

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Message-ID: <aO5YaR_B8ZYMdHa_@google.com>
Date: Tue, 14 Oct 2025 23:04:25 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf stat: Additional verbose details for <not
 supported> events

On Thu, Oct 09, 2025 at 06:31:51AM -0700, Ian Rogers wrote:
> On Wed, Oct 8, 2025 at 10:51 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Wed, Oct 08, 2025 at 09:31:53AM -0700, Ian Rogers wrote:
> > > On Wed, Oct 8, 2025 at 1:43 AM Namhyung Kim <namhyung@...nel.org> wrote:
> > > >
> > > > On Sun, Oct 05, 2025 at 11:14:21AM -0700, Ian Rogers wrote:
> > > > > If an event shows as "<not supported>" in perf stat output, in verbose
> > > > > mode add the strerror output to help diagnose the issue.
> > > > >
> > > > > Consider:
> > > > > ```
> > > > > $ perf stat -e cycles,data_read,instructions true
> > > > >
> > > > >  Performance counter stats for 'true':
> > > > >
> > > > >            357,457      cycles:u
> > > > >    <not supported> MiB  data_read:u
> > > > >            156,182      instructions:u                   #    0.44  insn per cycle
> > > > >
> > > > >        0.001250315 seconds time elapsed
> > > > >
> > > > >        0.001283000 seconds user
> > > > >        0.000000000 seconds sys
> > > > > ```
> > > > >
> > > > > To understand why the data_read uncore event failed, with this change:
> > > > > ```
> > > > > $ perf stat -v -e cycles,data_read,instructions true
> > > > > Using CPUID GenuineIntel-6-8D-1
> > > > > cycles -> cpu/cycles/
> > > > > data_read -> uncore_imc_free_running_0/data_read/
> > > > > data_read -> uncore_imc_free_running_1/data_read/
> > > > > instructions -> cpu/instructions/
> > > > > Control descriptor is not initialized
> > > > > Warning:
> > > > > kernel.perf_event_paranoid=2, trying to fall back to excluding kernel and hypervisor  samples
> > > > > Warning:
> > > > > kernel.perf_event_paranoid=2, trying to fall back to excluding kernel and hypervisor  samples
> > > > > Warning:
> > > > > kernel.perf_event_paranoid=2, trying to fall back to excluding kernel and hypervisor  samples
> > > > > Warning:
> > > > > data_read:u event is not supported by the kernel.
> > > > > Invalid event (data_read:u) in per-thread mode, enable system wide with '-a'.
> > > > > Warning:
> > > > > kernel.perf_event_paranoid=2, trying to fall back to excluding kernel and hypervisor  samples
> > > > > Warning:
> > > > > data_read:u event is not supported by the kernel.
> > > > > Invalid event (data_read:u) in per-thread mode, enable system wide with '-a'.
> > > > > cycles:u: 351621 362833 362833
> > > > > failed to read counter data_read:u
> > > > > failed to read counter data_read:u
> > > > > instructions:u: 156184 362833 362833
> > > > >
> > > > >  Performance counter stats for 'true':
> > > > >
> > > > >            351,621      cycles:u
> > > > >    <not supported> MiB  data_read:u
> > > > >            156,184      instructions:u                   #    0.44  insn per cycle
> > > > >
> > > > >        0.001584472 seconds time elapsed
> > > > >
> > > > >        0.001811000 seconds user
> > > > >        0.000000000 seconds sys
> > > > > ```
> > > > > where without this change only "data_read:u event is not supported by
> > > > > the kernel." is shown.
> > > >
> > > > I think what you say is:
> > > >
> > > > Before:
> > > >   data_read:u event is not supported by the kernel.
> > > >
> > > > After:
> > > >   data_read:u event is not supported by the kernel.
> > > >   Invalid event (data_read:u) in per-thread mode, enable system wide with '-a'.
> > >
> > > I kept things verbose as unfortunately the
> > > "kernel.perf_event_paranoid=2" is important as is the use of
> > > per-thread mode. Different paranoia levels lead to different errors
> > > and unfortunately a lot of the time the error gets reported as "
> > > data_read:u event is not supported by the kernel." and I'm not sure
> > > all users will get that the key part there is the :u modifier.
> >
> > Yep, I'm ok with the change.  But the changelog was a bit unclear what
> > is being added exactly.  IIUC we already have the paranoid message with
> > the verbose level 1.
> 
> I thought the line:
> """
> where without this change only "data_read:u event is not supported by
> the kernel." is shown.
> """
> covered this?

Yep, I've updated the commit log a little bit and applied to
perf-tools-next.

Thanks,
Namhyung