linux-kernel - Re: [PATCH v8 01/10] perf record --off-cpu: Add --off-cpu-thresh option

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Message-ID: <ZzutCSbEU-5UZXc3@google.com>
Date: Mon, 18 Nov 2024 13:09:29 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: acme@...nel.org, peterz@...radead.org, irogers@...gle.com,
	mingo@...hat.com, jolsa@...nel.org, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	James Clark <james.clark@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v8 01/10] perf record --off-cpu: Add --off-cpu-thresh
 option

Hello Howard,

On Tue, Nov 12, 2024 at 04:28:09PM -0800, Howard Chu wrote:
> Specify the threshold for dumping offcpu samples with --off-cpu-thresh,
> the unit is us (microsecond). Default value is 500000us (500ms, 0.5s).

I think it's better to add an option after you implemented the feature.
Before that you may hardcode the threshold if necessary.

Also it'd be a good practice to add an example for the option in the
commit message.

> 
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Howard Chu <howardchu95@...il.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: James Clark <james.clark@...aro.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lore.kernel.org/r/20241108204137.2444151-2-howardchu95@gmail.com
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/builtin-record.c | 26 ++++++++++++++++++++++++++
>  tools/perf/util/off_cpu.h   |  1 +
>  tools/perf/util/record.h    |  1 +

Please update the documentation if you add a new option.

Thanks,
Namhyung


>  3 files changed, 28 insertions(+)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index f83252472921..c069000efe5c 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -3149,6 +3149,28 @@ static int record__parse_mmap_pages(const struct option *opt,
>  	return ret;
>  }
>  
> +static int record__parse_off_cpu_thresh(const struct option *opt,
> +					const char *str,
> +					int unset __maybe_unused)
> +{
> +	struct record_opts *opts = opt->value;
> +	char *endptr;
> +	u64 off_cpu_thresh_us;
> +
> +	if (!str)
> +		return -EINVAL;
> +
> +	off_cpu_thresh_us = strtoull(str, &endptr, 10);
> +
> +	/* threshold isn't string "0", yet strtoull() returns 0, parsing failed */
> +	if (*endptr || (off_cpu_thresh_us == 0 && strcmp(str, "0")))
> +		return -EINVAL;
> +	else
> +		opts->off_cpu_thresh_us = off_cpu_thresh_us;
> +
> +	return 0;
> +}
> +
>  void __weak arch__add_leaf_frame_record_opts(struct record_opts *opts __maybe_unused)
>  {
>  }
> @@ -3342,6 +3364,7 @@ static struct record record = {
>  		.ctl_fd              = -1,
>  		.ctl_fd_ack          = -1,
>  		.synth               = PERF_SYNTH_ALL,
> +		.off_cpu_thresh_us   = OFFCPU_THRESH,
>  	},
>  };
>  
> @@ -3564,6 +3587,9 @@ static struct option __record_options[] = {
>  	OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"),
>  	OPT_STRING(0, "setup-filter", &record.filter_action, "pin|unpin",
>  		   "BPF filter action"),
> +	OPT_CALLBACK(0, "off-cpu-thresh", &record.opts, "us",
> +		     "Dump off-cpu samples if off-cpu time reaches this threshold. The unit is microsecond (default: 500000)",
> +		     record__parse_off_cpu_thresh),
>  	OPT_END()
>  };
>  
> diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h
> index 2dd67c60f211..c6edc0f7c40d 100644
> --- a/tools/perf/util/off_cpu.h
> +++ b/tools/perf/util/off_cpu.h
> @@ -16,6 +16,7 @@ struct record_opts;
>  			      PERF_SAMPLE_PERIOD | PERF_SAMPLE_CALLCHAIN | \
>  			      PERF_SAMPLE_CGROUP)
>  
> +#define OFFCPU_THRESH 500000ull
>  
>  #ifdef HAVE_BPF_SKEL
>  int off_cpu_prepare(struct evlist *evlist, struct target *target,
> diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h
> index a6566134e09e..2ca74add26c0 100644
> --- a/tools/perf/util/record.h
> +++ b/tools/perf/util/record.h
> @@ -79,6 +79,7 @@ struct record_opts {
>  	int	      synth;
>  	int	      threads_spec;
>  	const char    *threads_user_spec;
> +	u64	      off_cpu_thresh_us;
>  };
>  
>  extern const char * const *record_usage;
> -- 
> 2.43.0
>