linux-kernel - Re: [PATCH] perf record: Make logs more readable for event open failures

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Message-ID: <20260206163222.GH3529712@e132581.arm.com>
Date: Fri, 6 Feb 2026 16:32:22 +0000
From: Leo Yan <leo.yan@....com>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf record: Make logs more readable for event open
 failures

On Thu, Feb 05, 2026 at 02:33:04PM -0800, Ian Rogers wrote:
> On Thu, Feb 5, 2026 at 1:42 PM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> >
> > On Wed, Feb 04, 2026 at 09:29:14AM -0800, Ian Rogers wrote:
> > > On Wed, Feb 4, 2026 at 6:26 AM Leo Yan <leo.yan@....com> wrote:
> > > >
> > > > Since commit ee27476fa300 ("perf record: Skip don't fail for events that
> > > > don't open"), if a user does not have permission to access a PMU event,
> > > > perf reports:
> > > >
> > > >   perf record -e cs_etm// -C 3 -- ls
> > > >   Error:
> > > >   Failure to open event 'cs_etm//u' on PMU 'cs_etm' which will be removed.
> > > >   No fallback found for 'cs_etm//u' for error 13
> > > >   Error:
> > > >   Failure to open event 'dummy:u' on PMU 'software' which will be removed.
> > > >   No fallback found for 'dummy:u' for error 13
> > > >   Error:
> > > >   Failure to open any events for recording.
> > > >
> > > > The log is not very helpful, as no clear indication of what "error 13"
> > > > means or how to address the issue.
> > > >
> > > > This commit restores evsel__open_strerror() to generate a readable error
> > > > message and print it out:
> >
> > I'm applying this one, maybe we can at least suppress the one for dummy
> > when it is auto added?
> 
> IIRC it was left in as "perf record -e dummy" can be a way of just
> tracking sideband data and you'd want errors opening dummy to be
> warned upon in that case.

As Arnaldo said this patch has been picked, I sent a following patch
for simplifying the logs:
https://lore.kernel.org/linux-perf-users/20260206-perf_improve_log_for_open_event_failures-v1-1-366903bebcd7@arm.com/T/#u

If want me to resend two patches in a series, or squash into one,
please let me know.  Thanks!

Leo