[PATCH v9 01/10] perf record --off-cpu: Add --off-cpu-thresh option

[Howard Chu <howardchu95@gmail.com>]

Specify the threshold for dumping offcpu samples with --off-cpu-thresh,
the unit is us (microsecond). Default value is 500,000us (500ms, 0.5s).

Example:

  perf record --off-cpu --off-cpu-thresh 400000

The example above collects off-cpu samples whose off-cpu time is longer
than 400,000us

Suggested-by: Ian Rogers <irogers@google.com>
Suggested-by: Namhyung Kim <namhyung@kernel.org>
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Howard Chu <howardchu95@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241108204137.2444151-2-howardchu95@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/Documentation/perf-record.txt |  9 ++++++++
 tools/perf/builtin-record.c              | 26 ++++++++++++++++++++++++
 tools/perf/util/off_cpu.h                |  1 +
 tools/perf/util/record.h                 |  1 +
 4 files changed, 37 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 242223240a08..05c8977983de 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -829,6 +829,15 @@ filtered through the mask provided by -C option.
 	only, as of now.  So the applications built without the frame
 	pointer might see bogus addresses.
 
+	off-cpu profiling consists two types of samples: direct samples, which
+	share the same behavior as regular samples, and the accumulated
+	samples, stored in BPF stack trace map, presented after all the regular
+	samples.
+
+--off-cpu-thresh::
+	Once a task's off-cpu time reaches this threshold, it generates a
+	direct off-cpu sample.
+
 --setup-filter=<action>::
 	Prepare BPF filter to be used by regular users.  The action should be
 	either "pin" or "unpin".  The filter can be used after it's pinned.
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