perf tools: Add an option to multiplex counters in a single channel

Add an option to multiplex counters output in the channel of
the group leader, ie: the first counter opened:

	-M --multiplex

The effect is better serialized samples. This is especially
useful for tracepoint samples that need to be well serialized
for their post-processing.

Also make use of this option in 'perf sched'.

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

tools/perf/builtin-record.c

@@ -48,6 +48,7 @@ static int			call_graph			= 0;
 static int			inherit_stat			= 0;
 static int			no_samples			= 0;
 static int			sample_address			= 0;
+static int			multiplex			= 0;
 
 static long			samples;
 static struct timeval		last_read;
@@ -485,6 +486,9 @@ static void create_counter(int counter, int cpu, pid_t pid)
 		exit(-1);
 	}
 
+	if (multiplex && fd[nr_cpu][counter] != group_fd)
+		ioctl(fd[nr_cpu][counter], PERF_COUNTER_IOC_SET_OUTPUT, group_fd);
+
 	ioctl(fd[nr_cpu][counter], PERF_COUNTER_IOC_ENABLE);
 }
 
@@ -681,6 +685,8 @@ static const struct option options[] = {
 		    "Sample addresses"),
 	OPT_BOOLEAN('n', "no-samples", &no_samples,
 		    "don't sample"),
+	OPT_BOOLEAN('M', "multiplex", &multiplex,
+		    "multiplex counter output in a single channel"),
 	OPT_END()
 };
 

tools/perf/builtin-sched.c

@@ -1660,6 +1660,8 @@ static const char *record_args[] = {
 	"record",
 	"-a",
 	"-R",
+	"-M",
+	"-g",
 	"-c", "1",
 	"-e", "sched:sched_switch:r",
 	"-e", "sched:sched_stat_wait:r",