[PATCH v12 09/10] perf record --off-cpu: Add --off-cpu-thresh option

[Howard Chu]

Specify the threshold for dumping offcpu samples with --off-cpu-thresh,
the unit is milliseconds. Default value is 500ms.

Example:

  perf record --off-cpu --off-cpu-thresh 824

The example above collects off-cpu samples where the off-cpu time is
longer than 824ms

Suggested-by: Ian Rogers <irogers@xxxxxxxxxx>
Suggested-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Suggested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241108204137.2444151-2-howardchu95@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/Documentation/perf-record.txt |  9 ++++++++
 tools/perf/builtin-record.c              | 26 ++++++++++++++++++++++++
 tools/perf/util/bpf_off_cpu.c            |  3 +++
 tools/perf/util/off_cpu.h                |  1 +
 tools/perf/util/record.h                 |  1 +
 5 files changed, 40 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 242223240a08..f3ac4c739d5f 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 (in milliseconds), it
+	generates a direct off-cpu sample. The default is 500ms.
+
 --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 0b637cea4850..62183a6857f2 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -3147,6 +3147,28 @@ 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_ms; // converted to us for potential future improvements
+
+	if (!str)
+		return -EINVAL;
+
+	off_cpu_thresh_ms = strtoull(str, &endptr, 10);
+
+	/* the threshold isn't string "0", yet strtoull() returns 0, parsing failed */
+	if (*endptr || (off_cpu_thresh_ms == 0 && strcmp(str, "0")))
+		return -EINVAL;
+	else
+		opts->off_cpu_thresh_us = off_cpu_thresh_ms * USEC_PER_MSEC;
+
+	return 0;
+}
+
 void __weak arch__add_leaf_frame_record_opts(struct record_opts *opts __maybe_unused)
 {
 }
@@ -3340,6 +3362,7 @@ static struct record record = {
 		.ctl_fd              = -1,
 		.ctl_fd_ack          = -1,
 		.synth               = PERF_SYNTH_ALL,
+		.off_cpu_thresh_us   = OFFCPU_THRESH,
 	},
 };
 
@@ -3562,6 +3585,9 @@ 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, "ms",
+		     "Dump off-cpu samples if off-cpu time exceeds this threshold (in milliseconds). (Default: 500ms)",
+		     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 2e7e4ae43ffc..c3ac19393c0f 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -14,6 +14,7 @@
 #include "util/strlist.h"
 #include <bpf/bpf.h>
 #include <internal/xyarray.h>
+#include <linux/time64.h>
 
 #include "bpf_skel/off_cpu.skel.h"
 
@@ -286,6 +287,8 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
 		}
 	}
 
+	skel->bss->offcpu_thresh_ns = opts->off_cpu_thresh_us * NSEC_PER_USEC;
+
 	err = off_cpu_bpf__attach(skel);
 	if (err) {
 		pr_err("Failed to attach off-cpu BPF skeleton\n");
diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h
index 2a4b7f9b2c4c..f07ab2e36317 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_RAW | \
 			      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