linux-kernel - Re: [PATCH v1 1/4] perf stat: Allow no events to open if this is a "--null" run

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Message-ID: <aS5wjmbAM9ka3M2g@gmail.com>
Date: Tue, 2 Dec 2025 05:52:30 +0100
From: Ingo Molnar <mingo@...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>,
	Namhyung Kim <namhyung@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	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 v1 1/4] perf stat: Allow no events to open if this is a
 "--null" run

* Ingo Molnar <mingo@...nel.org> wrote:

> With all 4 patches applied to v6.18 'perf stat --null' 
> works fine:
> 
>   Tested-by: Ingo Molnar <mingo@...nel.org>

BTW., there's a long-standing perf-stat --repeat bug 
where signals don't seem to get properly propagated.

The following command takes 10 seconds to run, as 
expected:

  starship:~/tip> perf stat --null --repeat 10 sleep 1

   Performance counter stats for 'sleep 1' (10 runs):

           1.0026669 +- 0.0000503 seconds time elapsed  ( +-  0.01% )

But if I try to interrupt the test:

  starship:~/tip> perf stat --null --repeat 10 sleep 1
  ^Csleep: Interrupt
  ^Csleep: Interrupt

   Performance counter stats for 'sleep 1' (10 runs):

              0.9250 +- 0.0543 seconds time elapsed  ( +-  5.87% )

The Ctrl-C only propagates to the <command>, interrupts 
it (as can be seen from the shortened total runtime 
that is less than 10 seconds), and otherwise results in 
both an incorrect measurement and a misleading output 
of the partial results.

Furthermore, the test runs to full completion - which 
can be annoying if you happen to use high --repeat 
counts like I sometimes do. I have to Ctrl-Z and 
killall -9 perf to kill such instances.

Thanks,

	Ingo