linux-kernel - Re: [PATCH v2 1/2] perf tools: shortcut PERF_FLAG_FD

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Message-ID: <1443735136.3188.22.camel@opteya.com>
Date:	Thu, 01 Oct 2015 23:32:16 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...nel.org>,
	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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] perf tools: shortcut PERF_FLAG_FD_CLOEXEC
 probing in case of EBUSY error

Hi,

Le jeudi 01 octobre 2015 à 22:52 +0200, Jiri Olsa a écrit :
> On Thu, Oct 01, 2015 at 05:16:25PM +0200, Yann Droneaud wrote:
> > This patch is a simplification of the logic introduced as part of
> > commit 63914aca8f7e ('perf tools: Show better error message in case
> > we fail to open counters due to EBUSY error'):
> > if EBUSY is reported by perf_event_open(), it will not be possible
> > to probe PERF_FLAG_FD_CLOEXEC, so it's safe to leave early.
> > 
> > It should be noted that -EBUSY errors are not really expected here
> > since commit 038fa0b9739d ('perf tools: Fix PERF_FLAG_FD_CLOEXEC
> > flag probing event type open counters due to EBUSY error'):
> > the perf event type used now should be safe to use regarding -EBUSY
> > error.
> > 
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: David Ahern <dsahern@...il.com>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > 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>
> > Link: 
> > http://lkml.kernel.org/r/cover.1443708092.git.ydroneaud@opteya.com
> > Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
> > ---
> >  tools/perf/util/cloexec.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> > index 2babddaa2481..be226d293c91 100644
> > --- a/tools/perf/util/cloexec.c
> > +++ b/tools/perf/util/cloexec.c
> > @@ -56,7 +56,11 @@ static int perf_flag_probe(void)
> >  		return 1;
> >  	}
> >  
> > -	WARN_ONCE(err != EINVAL && err != EBUSY,
> > +	/* ignore busy errors */
> > +	if (err == EBUSY)
> > +		return -1;
> 
> so what's now the error message in case we get EBUSY ?
> 

None, just as it does currently.

perf_event_open_cloexec_flag() will still will return 0 just like
PERF_FLAG_FD_CLOEXEC was not available.

Handling -EBUSY is left to the function which will try to make use of
perf_event_open().

Regards.

-- 
Yann Droneaud
OPTEYA

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