linux-kernel - Re: [PATCH] perf stat: Poll for monitored tasks being alive

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Date:   Mon, 22 Oct 2018 11:56:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Jin Yao <yao.jin@...ux.intel.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf stat: Poll for monitored tasks being alive

Em Mon, Oct 22, 2018 at 11:30:15AM +0200, Jiri Olsa escreveu:
> Adding the check for tasks we monitor via -p/-t options,
> and finish stat if there's no longer task to monitor.

Wonder if instead of doing all those scnprintf, etc, we couldn't have a
perf ring buffer with a dummy event and then ask for PERF_RECORD_EXIT on
it, poll it, etc.

Thought about using getpgid(pid) but thagt also involves radix tree
lookups, so should also be more expensive than asking the kernel perf to
tell us about the exits.

Anyway, that can be done on top, if someone is interested, applying.

- Arnaldo
 
> Cc: Jin Yao <yao.jin@...ux.intel.com>
> Requested-by: Stephane Eranian <eranian@...gle.com>
> Link: http://lkml.kernel.org/n/tip-dfqvnvz0oqu5zg149aquz1jb@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/builtin-stat.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index b86aba1c8028..d1028d7755bb 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -409,6 +409,28 @@ static struct perf_evsel *perf_evsel__reset_weak_group(struct perf_evsel *evsel)
>  	return leader;
>  }
>  
> +static bool is_target_alive(struct target *_target,
> +			    struct thread_map *threads)
> +{
> +	struct stat st;
> +	int i;
> +
> +	if (!target__has_task(_target))
> +		return true;
> +
> +	for (i = 0; i < threads->nr; i++) {
> +		char path[PATH_MAX];
> +
> +		scnprintf(path, PATH_MAX, "%s/%d", procfs__mountpoint(),
> +			  threads->map[i].pid);
> +
> +		if (!stat(path, &st))
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  {
>  	int interval = stat_config.interval;
> @@ -579,6 +601,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  		enable_counters();
>  		while (!done) {
>  			nanosleep(&ts, NULL);
> +			if (!is_target_alive(&target, evsel_list->threads))
> +				break;
>  			if (timeout)
>  				break;
>  			if (interval) {
> -- 
> 2.17.2