perf stat: Don't print bogus data on -e cycles

When only the cycles event is requested:

$ perf stat -e cycles dd if=/dev/zero of=/dev/null count=1000000
1000000+0 records in
1000000+0 records out
512000000 bytes (512 MB) copied, 0.26123 s, 2.0 GB/s

 Performance counter stats for 'dd if=/dev/zero of=/dev/null count=1000000':

       911,626,453 cycles                    #    0.000 GHz

       0.262113350 seconds time elapsed

The 0.000 GHz comment in the output is totally bogus and misleading. It
happens because update_shadow_stats() doesn't touch runtime_nsecs_stats;
it is only written when a requested counter matches a SW_TASK_CLOCK. In
our case, since we have only requested HW_CPU_CYCLES,
runtime_nsecs_stats is unavailable. So, omit printing the comment
altogether.
Signed-off-by: NRamkumar Ramachandra <artagnon@gmail.com>
Acked-by: NIngo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1380539585-23859-3-git-send-email-artagnon@gmail.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-stat.c

@@ -997,10 +997,10 @@ static void abs_printout(int cpu, int nr, struct perf_evsel *evsel, double avg)
 	} else if (perf_evsel__match(evsel, HARDWARE, HW_CPU_CYCLES)) {
 		total = avg_stats(&runtime_nsecs_stats[cpu]);
 
-		if (total)
-			ratio = 1.0 * avg / total;
-
-		fprintf(output, " # %8.3f GHz                    ", ratio);
+		if (total) {
+			ratio = avg / total;
+			fprintf(output, " # %8.3f GHz                    ", ratio);
+		}
 	} else if (transaction_run &&
 		   perf_evsel__cmp(evsel, nth_evsel(T_CYCLES_IN_TX))) {
 		total = avg_stats(&runtime_cycles_stats[cpu]);