Commit 3e76ac78 authored Dec 20, 2011 by Andrew Vagin Committed by Arnaldo Carvalho de Melo Dec 20, 2011

perf record: Add ability to record event period



The problem is that when SAMPLE_PERIOD is not set, the kernel generates
a number of samples in proportion to an event's period. Number of these
samples may be too big and the kernel throttles all samples above a
defined limit.

E.g.: I want to trace when a process sleeps. I created a process which
sleeps for 1ms and for 4ms.  perf got 100 events in both cases.

swapper 0 [000] 1141.371830: sched_stat_sleep: comm=foo pid=1801 delay=1386750 [ns]
swapper 0 [000] 1141.369444: sched_stat_sleep: comm=foo pid=1801 delay=4499585 [ns]

In the first case a kernel want to send 4499585 events and in the second
case it wants to send 1386750 events.  perf-reports shows that process
sleeps in both places equal time.

Instead of this we can get only one sample with an attribute period. As
result we have less data transferring between kernel and user-space and
we avoid throttling of samples.

The patch "events: Don't divide events if it has field period" added a
kernel part of this functionality.

Acked-by: Arun Sharma <asharma@fb.com>
Cc: Arun Sharma <asharma@fb.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: devel@openvz.org
Link: http://lkml.kernel.org/r/1324391565-1369947-1-git-send-email-avagin@openvz.org


Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

parent 124ba940

tools/perf/builtin-record.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -700,6 +700,7 @@ const struct option record_options[] = {
		OPT_BOOLEAN('d', "data", &record.opts.sample_address,
		"Sample addresses"),
		OPT_BOOLEAN('T', "timestamp", &record.opts.sample_time, "Sample timestamps"),
		OPT_BOOLEAN('P', "period", &record.opts.period, "Sample period"),
		OPT_BOOLEAN('n', "no-samples", &record.opts.no_samples,
		"don't sample"),
		OPT_BOOLEAN('N', "no-buildid-cache", &record.no_buildid_cache,

tools/perf/perf.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -200,6 +200,7 @@ struct perf_record_opts {
		bool sample_time;
		bool sample_id_all_avail;
		bool system_wide;
		bool period;
		unsigned int freq;
		unsigned int mmap_pages;
		unsigned int user_freq;

tools/perf/util/evsel.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -108,6 +108,9 @@ void perf_evsel__config(struct perf_evsel evsel, struct perf_record_opts opts)
		if (opts->system_wide)
		attr->sample_type \|= PERF_SAMPLE_CPU;

		if (opts->period)
		attr->sample_type \|= PERF_SAMPLE_PERIOD;

		if (opts->sample_id_all_avail &&
		(opts->sample_time \|\| opts->system_wide \|\|
		!opts->no_inherit \|\| opts->cpu_list))

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