perf python: Make twatch.py use soft dummy event, freq=0

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@redhat.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jaroslav Skarvada <jskarvad@redhat.com>
Cc: Jeremy Eder <jeder@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-kfsijirfrs6xfhkcdxeoen06@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 11 insertions, 1 deletions

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)