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From:   Stephen Brennan <stephen.s.brennan@oracle.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>
Cc:     Stephen Brennan <stephen.s.brennan@oracle.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] perf script python: Allow reporting [un]throttle
Date:   Wed,  1 Sep 2021 14:08:15 -0700
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perf_events may sometimes throttle an event due to creating too many
samples during a given timer tick. As of now, the perf tool will not
report on throttling, which means this is a silent error. Implement a
callback for the throttle and unthrottle events within the Python
scripting engine, which can allow scripts to detect and report when
events may have been lost due to throttling. The simplest script to
report throttle events is:

def throttle(*args):
    print("throttle" + repr(args))
def unthrottle(*args):
    print("unthrottle" + repr(args))

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---
 tools/perf/builtin-script.c                   | 13 ++++++++
 .../scripting-engines/trace-event-python.c    | 32 +++++++++++++++++++
 tools/perf/util/trace-event.h                 |  3 ++
 3 files changed, 48 insertions(+)

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 064da7f3618d..072869a35f85 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -2492,6 +2492,17 @@ process_lost_event(struct perf_tool *tool,
 			   sample->tid);
 }
 
+static int
+process_throttle_event(struct perf_tool *tool __maybe_unused,
+		       union perf_event *event,
+		       struct perf_sample *sample,
+		       struct machine *machine)
+{
+	if (scripting_ops && scripting_ops->process_throttle)
+		scripting_ops->process_throttle(event, sample, machine);
+	return 0;
+}
+
 static int
 process_finished_round_event(struct perf_tool *tool __maybe_unused,
 			     union perf_event *event,
@@ -3652,6 +3663,8 @@ int cmd_script(int argc, const char **argv)
 			.stat_config	 = process_stat_config_event,
 			.thread_map	 = process_thread_map_event,
 			.cpu_map	 = process_cpu_map_event,
+			.throttle	 = process_throttle_event,
+			.unthrottle	 = process_throttle_event,
 			.ordered_events	 = true,
 			.ordering_requires_timestamps = true,
 		},
diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index 69129e2aa7a1..c0c010350bc2 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -1422,6 +1422,37 @@ static void python_process_event(union perf_event *event,
 	}
 }
 
+static void python_process_throttle(union perf_event *event,
+				    struct perf_sample *sample,
+				    struct machine *machine)
+{
+	const char *handler_name;
+	PyObject *handler, *t;
+
+	if (event->header.type == PERF_RECORD_THROTTLE)
+		handler_name = "throttle";
+	else
+		handler_name = "unthrottle";
+	handler = get_handler(handler_name);
+	if (!handler)
+		return;
+
+	t = tuple_new(6);
+	if (!t)
+		return;
+
+	tuple_set_u64(t, 0, event->throttle.time);
+	tuple_set_u64(t, 1, event->throttle.id);
+	tuple_set_u64(t, 2, event->throttle.stream_id);
+	tuple_set_s32(t, 3, sample->cpu);
+	tuple_set_s32(t, 4, sample->pid);
+	tuple_set_s32(t, 5, sample->tid);
+
+	call_object(handler, t, handler_name);
+
+	Py_DECREF(t);
+}
+
 static void python_do_process_switch(union perf_event *event,
 				     struct perf_sample *sample,
 				     struct machine *machine)
@@ -2079,5 +2110,6 @@ struct scripting_ops python_scripting_ops = {
 	.process_auxtrace_error	= python_process_auxtrace_error,
 	.process_stat		= python_process_stat,
 	.process_stat_interval	= python_process_stat_interval,
+	.process_throttle	= python_process_throttle,
 	.generate_script	= python_generate_script,
 };
diff --git a/tools/perf/util/trace-event.h b/tools/perf/util/trace-event.h
index 54aadeedf28c..640981105788 100644
--- a/tools/perf/util/trace-event.h
+++ b/tools/perf/util/trace-event.h
@@ -90,6 +90,9 @@ struct scripting_ops {
 	void (*process_stat)(struct perf_stat_config *config,
 			     struct evsel *evsel, u64 tstamp);
 	void (*process_stat_interval)(u64 tstamp);
+	void (*process_throttle)(union perf_event *event,
+				 struct perf_sample *sample,
+				 struct machine *machine);
 	int (*generate_script) (struct tep_handle *pevent, const char *outfile);
 };
 
-- 
2.30.2