perf record --off-cpu: Add --off-cpu-thresh option

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 direct off-cpu samples where the off-cpu time is longer than 824ms. Committer testing: After commenting out the end off-cpu dump to have just the ones that are added right after the task is scheduled back, and using a threshould of 1000ms, we see some periods (the 5th column, just before "offcpu-time" in the 'perf script' output) that are over 1000.000.000 nanoseconds: root@number:~# perf record --off-cpu --off-cpu-thresh 10000 ^C[ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 3.902 MB perf.data (34335 samples) ] root@number:~# perf script <SNIP> Isolated Web Co 59932 [028] 63839.594437: 1000049427 offcpu-time: 7fe63c7976c2 __syscall_cancel_arch_end+0x0 (/usr/lib64/libc.so.6) 7fe63c78c04c __futex_abstimed_wait_common+0x7c (/usr/lib64/libc.so.6) 7fe63c78e928 pthread_cond_timedwait@@GLIBC_2.3.2+0x178 (/usr/lib64/libc.so.6) 5599974a9fe7 mozilla::detail::ConditionVariableImpl::wait_for(mozilla::detail::MutexImpl&, mozilla::BaseTimeDuration<mozilla::TimeDurationValueCalculator> const&)+0xe7 (/usr/lib64/fir> 100000000 [unknown] ([unknown]) swapper 0 [025] 63839.594459: 195724 cycles:P: ffffffffac328270 read_tsc+0x0 ([kernel.kallsyms]) Isolated Web Co 59932 [010] 63839.594466: 1000055278 offcpu-time: 7fe63c7976c2 __syscall_cancel_arch_end+0x0 (/usr/lib64/libc.so.6) 7fe63c78ba24 __syscall_cancel+0x14 (/usr/lib64/libc.so.6) 7fe63c804c4e __poll+0x1e (/usr/lib64/libc.so.6) 7fe633b0d1b8 PollWrapper(_GPollFD*, unsigned int, int) [clone .lto_priv.0]+0xf8 (/usr/lib64/firefox/libxul.so) 10000002c [unknown] ([unknown]) swapper 0 [027] 63839.594475: 134433 cycles:P: ffffffffad4c45d9 irqentry_enter+0x19 ([kernel.kallsyms]) swapper 0 [028] 63839.594499: 215838 cycles:P: ffffffffac39199a switch_mm_irqs_off+0x10a ([kernel.kallsyms]) MediaPD~oder #1 1407676 [027] 63839.594514: 134433 cycles:P: 7f982ef5e69f dct_IV(int*, int, int*)+0x24f (/usr/lib64/libfdk-aac.so.2.0.0) swapper 0 [024] 63839.594524: 267411 cycles:P: ffffffffad4c6ee6 poll_idle+0x56 ([kernel.kallsyms]) MediaSu~sor #75 1093827 [026] 63839.594555: 332652 cycles:P: 55be753ad030 moz_xmalloc+0x200 (/usr/lib64/firefox/firefox) swapper 0 [027] 63839.594616: 160548 cycles:P: ffffffffad144840 menu_select+0x570 ([kernel.kallsyms]) Isolated Web Co 14019 [027] 63839.595120: 1000050178 offcpu-time: 7fc9537cc6c2 __syscall_cancel_arch_end+0x0 (/usr/lib64/libc.so.6) 7fc9537c104c __futex_abstimed_wait_common+0x7c (/usr/lib64/libc.so.6) 7fc9537c3928 pthread_cond_timedwait@@GLIBC_2.3.2+0x178 (/usr/lib64/libc.so.6) 7fc95372a3c8 pt_TimedWait+0xb8 (/usr/lib64/libnspr4.so) 7fc95372a8d8 PR_WaitCondVar+0x68 (/usr/lib64/libnspr4.so) 7fc94afb1f7c WatchdogMain(void*)+0xac (/usr/lib64/firefox/libxul.so) 7fc947498660 [unknown] ([unknown]) 7fc9535fce88 [unknown] ([unknown]) 7fc94b620e60 WatchdogManager::~WatchdogManager()+0x0 (/usr/lib64/firefox/libxul.so) fff8548387f8b48 [unknown] ([unknown]) swapper 0 [003] 63839.595712: 212948 cycles:P: ffffffffacd5b865 acpi_os_read_port+0x55 ([kernel.kallsyms]) <SNIP> Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Suggested-by: Ian Rogers <irogers@google.com> Suggested-by: Namhyung Kim <namhyung@kernel.org> Reviewed-by: Ian Rogers <irogers@google.com> Signed-off-by: Howard Chu <howardchu95@gmail.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Tested-by: Gautam Menghani <gautam@linux.ibm.com> Tested-by: Ian Rogers <irogers@google.com> Acked-by: Namhyung Kim <namhyung@kernel.org> 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: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/20241108204137.2444151-2-howardchu95@gmail.com Link: https://lore.kernel.org/r/20250501022809.449767-10-howardchu95@gmail.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2025-05-05 21:51:54 -03:00
parent 74069a0160
commit 9557c00076
6 changed files with 41 additions and 1 deletions
@@ -842,6 +842,15 @@ 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.
@@ -3162,6 +3162,28 @@ out_free:
 	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;
+
+	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_ns = off_cpu_thresh_ms * NSEC_PER_MSEC;
+
+	return 0;
+}
+
 void __weak arch__add_leaf_frame_record_opts(struct record_opts *opts __maybe_unused)
 {
 }
@@ -3355,6 +3377,7 @@ static struct record record = {
 		.ctl_fd              = -1,
 		.ctl_fd_ack          = -1,
 		.synth               = PERF_SYNTH_ALL,
+		.off_cpu_thresh_ns   = OFFCPU_THRESH,
 	},
 };

@@ -3582,6 +3605,9 @@ 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()
 };

@@ -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"

@@ -292,6 +293,8 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
 		}
 	}

+	skel->bss->offcpu_thresh_ns = opts->off_cpu_thresh_ns;
+
 	err = off_cpu_bpf__attach(skel);
 	if (err) {
 		pr_err("Failed to attach off-cpu BPF skeleton\n");
@@ -124,7 +124,7 @@ const volatile bool uses_cgroup_v1 = false;

 int perf_subsys_id = -1;

-__u64 offcpu_thresh_ns = 500000000ull;
+__u64 offcpu_thresh_ns;

 /*
 * Old kernel used to call it task_struct->state and now it's '__state'.
@@ -16,6 +16,7 @@ struct record_opts;
 			      PERF_SAMPLE_PERIOD | PERF_SAMPLE_RAW | \
 			      PERF_SAMPLE_CGROUP)

+#define OFFCPU_THRESH 500000000ULL

 #ifdef HAVE_BPF_SKEL
 int off_cpu_prepare(struct evlist *evlist, struct target *target,
@@ -80,6 +80,7 @@ struct record_opts {
 	int	      synth;
 	int	      threads_spec;
 	const char    *threads_user_spec;
+	u64	      off_cpu_thresh_ns;
 };

 extern const char * const *record_usage;