linux-kernel - Re: [PATCH v6 2/8] perf record --off-cpu: Add --off-cpu-thresh

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Message-ID: <Zvo5weauCaaKQQ8b@google.com>
Date: Sun, 29 Sep 2024 22:40:17 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/8] perf record --off-cpu: Add --off-cpu-thresh

On Fri, Sep 27, 2024 at 01:27:30PM -0700, Howard Chu wrote:
> Add the --off-cpu-thresh argument to specify the off-cpu time threshold.
> If the off-cpu time exceeds this threshold, dump the off-cpu data
> directly.
> 
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Howard Chu <howardchu95@...il.com>
> ---
>  tools/perf/builtin-record.c            | 26 ++++++++++++++++++++++++++
>  tools/perf/util/bpf_off_cpu.c          |  2 ++
>  tools/perf/util/bpf_skel/off_cpu.bpf.c |  2 ++
>  tools/perf/util/off_cpu.h              |  2 ++
>  tools/perf/util/record.h               |  1 +
>  5 files changed, 33 insertions(+)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index adbaf80b398c..bd53fb3c98ec 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;
> +
> +	if (!str)
> +		return -EINVAL;
> +
> +	off_cpu_thresh = strtoul(str, &endptr, 10);

Do you mean strtoull() ?


> +
> +	/* threshold isn't string "0", yet strtoull() returns 0, parsing failed */
> +	if (*endptr || (off_cpu_thresh == 0 && strcmp(str, "0")))
> +		return -EINVAL;
> +	else
> +		opts->off_cpu_thresh = off_cpu_thresh;
> +
> +	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      = OFF_CPU_THRESH_DEFAULT,
>  	},
>  };
>  
> @@ -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/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
> index a590a8ac1f9d..eaef643f50e3 100644
> --- a/tools/perf/util/bpf_off_cpu.c
> +++ b/tools/perf/util/bpf_off_cpu.c
> @@ -272,6 +272,8 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
>  		}
>  	}
>  
> +	skel->bss->offcpu_thresh = opts->off_cpu_thresh * 1000;
> +
>  	err = off_cpu_bpf__attach(skel);
>  	if (err) {
>  		pr_err("Failed to attach off-cpu BPF skeleton\n");
> diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> index c152116df72f..5ea320aa9a53 100644
> --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
> +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> @@ -97,6 +97,8 @@ const volatile bool uses_cgroup_v1 = false;
>  
>  int perf_subsys_id = -1;
>  
> +__u64 sample_id, sample_type, offcpu_thresh;

The sample_id and sample_type aren't used in the patch.

Thanks,
Namhyung

> +
>  /*
>   * Old kernel used to call it task_struct->state and now it's '__state'.
>   * Use BPF CO-RE "ignored suffix rule" to deal with it like below:
> diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h
> index 2dd67c60f211..357231cb1c38 100644
> --- a/tools/perf/util/off_cpu.h
> +++ b/tools/perf/util/off_cpu.h
> @@ -10,6 +10,8 @@ struct record_opts;
>  
>  #define OFFCPU_EVENT  "offcpu-time"
>  
> +#define OFF_CPU_THRESH_DEFAULT 500000ull
> +
>  #define OFFCPU_SAMPLE_TYPES  (PERF_SAMPLE_IDENTIFIER | PERF_SAMPLE_IP | \
>  			      PERF_SAMPLE_TID | PERF_SAMPLE_TIME | \
>  			      PERF_SAMPLE_ID | PERF_SAMPLE_CPU | \
> diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h
> index a6566134e09e..3c11416e6627 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;
>  };
>  
>  extern const char * const *record_usage;
> -- 
> 2.43.0
>