perf report: Print out the total number of events

So that the statistical quality of the profile can be estimated at a glance.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-report.c

@@ -721,6 +721,8 @@ static size_t output__fprintf(FILE *fp, uint64_t total_samples)
 	struct rb_node *nd;
 	size_t ret = 0;
 
+	fprintf(fp, "#\n");
+	fprintf(fp, "# (%Ld profiler events)\n", (__u64)total_samples);
 	fprintf(fp, "#\n");
 
 	fprintf(fp, "# Overhead");