linux-kernel - Re: [PATCH 2/5] perf record: Add error message for EMFILE

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Message-ID: <4F256587.3090504@gmail.com>
Date:	Sun, 29 Jan 2012 08:28:07 -0700
From:	David Ahern <dsahern@...il.com>
To:	Namhyung Kim <namhyung@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] perf record: Add error message for EMFILE



On 01/29/2012 01:55 AM, Namhyung Kim wrote:
> When a user tries to open so many events, perf_event_oen syscall
> may fail with EMFILE. Provide an advice for that case.
> 
> Signed-off-by: Namhyung Kim <namhyung@...il.com>
> ---
>  tools/perf/builtin-record.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 32870eef952f..5d3b6794d93b 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -249,6 +249,10 @@ try_again:
>  				ui__warning("The %s event is not supported.\n",
>  					    event_name(pos));
>  				exit(EXIT_FAILURE);
> +			} else if (err == EMFILE) {
> +				ui__warning("Too many events are opened.\n"
> +					    "Try again after reducing the number of events.\n");
> +				exit(EXIT_FAILURE);
>  			}
>  
>  			printf("\n");

It's not just the number of events: an fd is opened for each specified
event on each specified cpu and for each specified task. See
__perf_evsel__open(). e.g., the new --uid option on a 16 cpu server can
hit the limit pretty fast.

David
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