linux-kernel - Re: [PATCH] perf tools: Show better error message in case we fail to open counters due to EBUSY error

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Date:	Sat, 02 Aug 2014 19:58:25 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	William Cohen <wcohen@...hat.com>, ydroneaud@...eya.com
Subject: Re: [PATCH] perf tools: Show better error message in case we fail
 to open counters due to EBUSY error

Hi Jiri,

Le vendredi 01 août 2014 à 17:46 +0200, Jiri Olsa a écrit :
> Showing better error message in case we fail to open
> counters due to the EBUSY error. If we detect oprofile
> daemon process running, we now display following message
> for EBUSY error:
> 
>   $ perf record ls
>   Error:
>   The PMU counters are busy/taken by another profiler.
>   We found oprofile daemon running, please stop it and try again.
> 
> In case oprofiled was not detected the current error
> message stays:
> 
>   $ perf record ls
>   Error:
>   The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles).
>   /bin/dmesg may provide additional information.
>   No CONFIG_PERF_EVENTS=y kernel support configured?
> 
> Also changing PERF_FLAG_FD_CLOEXEC detection code not to display
> error in case of EBUSY error, as it currently does:
> 
>   $ perf record ls
>   Error:
>   perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error 16 (Device or resource busy)
>   perf_event_open(..., 0) failed unexpectedly with error 16 (Device or resource busy)
>   The PMU counters are busy/taken by another profiler.
>   We found oprofile daemon running, please stop it and try again.
> 
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Namhyung Kim <namhyung@...il.com>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: William Cohen <wcohen@...hat.com>
> Cc: Yann Droneaud <ydroneaud@...eya.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/util/cloexec.c |  4 ++--
>  tools/perf/util/evsel.c   |  6 ++++++
>  tools/perf/util/util.c    | 36 ++++++++++++++++++++++++++++++++++++
>  tools/perf/util/util.h    |  1 +
>  4 files changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> index c5d05ec17220..dede0c388ed4 100644
> --- a/tools/perf/util/cloexec.c
> +++ b/tools/perf/util/cloexec.c
> @@ -25,7 +25,7 @@ static int perf_flag_probe(void)
>  		return 1;
>  	}
>  
> -	WARN_ONCE(err != EINVAL,
> +	WARN_ONCE(err != EINVAL && err != EBUSY,
>  		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
>  		  err, strerror(err));
>  
> @@ -33,7 +33,7 @@ static int perf_flag_probe(void)
>  	fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
>  	err = errno;
>  
> -	if (WARN_ONCE(fd < 0,
> +	if (WARN_ONCE(fd < 0 && err != EBUSY,
>  		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
>  		      err, strerror(err)))
>  		return -1;

It's definitely possible to shortcut the function if EBUSY is returned
by first call to perf_event_open().

diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
index dc360ebde745..d5c626d5432a 100644
--- a/tools/perf/util/cloexec.c
+++ b/tools/perf/util/cloexec.c
@@ -25,6 +25,9 @@ static int perf_flag_probe(void)
 		return 1;
 	}
 
+	if (err == EBUSY)
+		return -1;
+
 	WARN_ONCE(err != EINVAL,
 		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
 		  err, strerror(err));


BTW, I'm going to submit a patch to make the function report such 
warning only once.

Regards.

-- 
Yann Droneaud
OPTEYA


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