linux-kernel - [PATCH 04/10] perf python: Make twatch.py use soft dummy event, freq=0

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Message-Id: <1438273028-5191-5-git-send-email-acme@kernel.org>
Date:	Thu, 30 Jul 2015 13:17:02 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jaroslav Skarvada <jskarvad@...hat.com>,
	Jeremy Eder <jeder@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: [PATCH 04/10] perf python: Make twatch.py use soft dummy event, freq=0

From: Arnaldo Carvalho de Melo <acme@...hat.com>

To not sample, what we want are just the PERF_RECORD_ lifetime events
for threads, using the default, PERF_TYPE_HARDWARE +
PERF_COUNT_HW_CYCLES and freq=1 (the default), makes perf reenable
irq_vectors:local_timer_entry, disabling nohz, not good for some use
cases where all we want is to get notifications when threads comes and
goes...

Fix it by using PERF_TYPE_SOFTWARE (no counter rotation) and
PERF_COUNT_SW_DUMMY (created by Adrian so that we could have access to
those PERF_RECORD_ goodies).

Reported-by: Luiz Fernando Capitulino <lcapitulino@...hat.com>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: David Ahern <dsahern@...il.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jaroslav Skarvada <jskarvad@...hat.com>
Cc: Jeremy Eder <jeder@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Stephane Eranian <eranian@...gle.com>
Link: http://lkml.kernel.org/n/tip-kfsijirfrs6xfhkcdxeoen06@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/python/twatch.py | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/perf/python/twatch.py b/tools/perf/python/twatch.py
index 2225162ee1fc..b9d508336ae6 100755
--- a/tools/perf/python/twatch.py
+++ b/tools/perf/python/twatch.py
@@ -18,10 +18,20 @@ import perf
 def main():
 	cpus = perf.cpu_map()
 	threads = perf.thread_map()
-	evsel = perf.evsel(task = 1, comm = 1, mmap = 0,
+	evsel = perf.evsel(type	  = perf.TYPE_SOFTWARE,
+			   config = perf.COUNT_SW_DUMMY,
+			   task = 1, comm = 1, mmap = 0, freq = 0,
 			   wakeup_events = 1, watermark = 1,
 			   sample_id_all = 1,
 			   sample_type = perf.SAMPLE_PERIOD | perf.SAMPLE_TID | perf.SAMPLE_CPU)
+
+	"""What we want are just the PERF_RECORD_ lifetime events for threads,
+	 using the default, PERF_TYPE_HARDWARE + PERF_COUNT_HW_CYCLES & freq=1
+	 (the default), makes perf reenable irq_vectors:local_timer_entry, when
+	 disabling nohz, not good for some use cases where all we want is to get
+	 threads comes and goes... So use (perf.TYPE_SOFTWARE, perf_COUNT_SW_DUMMY,
+	 freq=0) instead."""
+
 	evsel.open(cpus = cpus, threads = threads);
 	evlist = perf.evlist(cpus, threads)
 	evlist.add(evsel)
-- 
2.1.0

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