perf evlist: Be more specific on -F/--freq

Currently perf evlist -F shows the number as if it's always sampling
frequency.  But we now support per-event freq/period settings.  So it'd
better to show more detailed info whether it's freq or period.

  $ perf record -e 'cpu/config=1/,cpu/config=2,period=300000/' sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.017 MB perf.data ]

  $ perf evlist -F
  cpu/config=1/: sample_freq=4000
  cpu/config=2,period=300000/: sample_period=300000

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1439102724-14079-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -2158,8 +2158,13 @@ int perf_evsel__fprintf(struct perf_evsel *evsel,
 		printed += perf_event_attr__fprintf(fp, &evsel->attr,
 						    __print_attr__fprintf, &first);
 	} else if (details->freq) {
-		printed += comma_fprintf(fp, &first, " sample_freq=%" PRIu64,
-					 (u64)evsel->attr.sample_freq);
+		const char *term = "sample_freq";
+
+		if (!evsel->attr.freq)
+			term = "sample_period";
+
+		printed += comma_fprintf(fp, &first, " %s=%" PRIu64,
+					 term, (u64)evsel->attr.sample_freq);
 	}
 out:
 	fputc('\n', fp);