linux-kernel - Re: [patch] perf tools: perf list broken on ARM

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Date:	Wed, 8 Jan 2014 16:30:17 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
	Chad Paradis <chad.paradis@...t.maine.edu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [patch] perf tools: perf list broken on ARM


just checking on the status of this patch.  Am I sending it to the wrong 
place?  Did it get lost in the post-holiday e-mail purges?  

The bug is annoying if you're trying to use perf on ARM systems.

Vince

On Mon, 30 Dec 2013, Vince Weaver wrote:

> 
> "perf list" listing of hardware events doesn't work on older ARM devices.
> The change enabling event detection:
> 
>  commit b41f1cec91c37eeea6fdb15effbfa24ea0a5536b
>  Author: Namhyung Kim <namhyung.kim@....com>
>  Date:   Tue Aug 27 11:41:53 2013 +0900
> 
>      perf list: Skip unsupported events
> 
> 
> uses the following code in tools/perf/util/parse-events.c:
> 
>         struct perf_event_attr attr = {
>                 .type = type,
>                 .config = config,
>                 .disabled = 1,
>                 .exclude_kernel = 1,
>         };
> 
> On ARM machines pre-dating the Cortex-A15 this doesn't work, as
> these machines don't support .exclude_kernel.  So starting with 3.12
> "perf list" does not report any hardware events at all on older
> machines (seen on Rasp-Pi, Pandaboard, Beagleboard, etc).
> 
> This version of the patch makes changes suggested by Namhyung Kim
> to check for EACCESS and retry (instead of just dropping
> the exclude_kernel) so we can properly handle machines where 
> /proc/sys/kernel/perf_event_paranoid is set to 2.
> 
> Reported-by: Chad Paradis <chad.paradis@...t.maine.edu>
> Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
> Acked-by: Namhyung Kim <namhyung@...nel.org>
> 
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 6de6f89..1fa98b9 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -1082,12 +1082,12 @@ int is_valid_tracepoint(const char *event_string)
>  static bool is_event_supported(u8 type, unsigned config)
>  {
>  	bool ret = true;
> +	int open_return;
>  	struct perf_evsel *evsel;
>  	struct perf_event_attr attr = {
>  		.type = type,
>  		.config = config,
>  		.disabled = 1,
> -		.exclude_kernel = 1,
>  	};
>  	struct {
>  		struct thread_map map;
> @@ -1099,7 +1099,20 @@ static bool is_event_supported(u8 type, unsigned config)
>  
>  	evsel = perf_evsel__new(&attr);
>  	if (evsel) {
> -		ret = perf_evsel__open(evsel, NULL, &tmap.map) >= 0;
> +		open_return = perf_evsel__open(evsel, NULL, &tmap.map);
> +		ret = open_return >= 0;
> +
> +		if (open_return == -EACCES) {
> +			/*
> +			 * This happens if the paranoid value
> +			 * /proc/sys/kernel/perf_event_paranoid is set to 2
> +			 * Re-run with exclude_kernel set; we don't do that
> +			 * by default as some ARM machines do not support it.
> +			 *
> +			 */
> +			evsel->attr.exclude_kernel = 1;
> +			ret = perf_evsel__open(evsel, NULL, &tmap.map) >= 0;
> +		}
>  		perf_evsel__delete(evsel);
>  	}
>  
> 

Vince Weaver
vincent.weaver@...ne.edu
http://www.eece.maine.edu/~vweaver/
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