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

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Date:	Fri, 2 Oct 2015 15:19:19 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Yann Droneaud <ydroneaud@...eya.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

On Thu, Oct 01, 2015 at 11:32:16PM +0200, Yann Droneaud wrote:
> 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().

I see, ook

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka
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