perf: Make the trace events sample period default to 1

Trace events are mostly used for tracing and then require not to
be lost when possible. As opposite to hardware events that really
require to trigger after a given sample period, trace events mostly
need to trigger everytime.

It is a frustrating experience to trace with perf and realize we
lost a lot of events because we forgot the "-c 1" option.

Then default sample_period to 1 for trace events but let the user
override it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>

tools/perf/util/parse-events.c

@@ -422,6 +422,8 @@ parse_single_tracepoint_event(char *sys_name,
 	attr->sample_type |= PERF_SAMPLE_TIME;
 	attr->sample_type |= PERF_SAMPLE_CPU;
 
+	attr->sample_period = 1;
+
 	snprintf(evt_path, MAXPATHLEN, "%s/%s/%s/id", debugfs_path,
 		 sys_name, evt_name);