linux-kernel - [PATCH 2/2] perf stat: Also hide metric from JSON if units are an empty string

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Message-Id: <20241025090307.59127-3-james.clark@linaro.org>
Date: Fri, 25 Oct 2024 10:03:05 +0100
From: James Clark <james.clark@...aro.org>
To: linux-perf-users@...r.kernel.org,
	acme@...nel.org,
	namhyung@...nel.org,
	irogers@...gle.com,
	tim.c.chen@...ux.intel.com
Cc: James Clark <james.clark@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Yicong Yang <yangyicong@...ilicon.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] perf stat: Also hide metric from JSON if units are an empty string

We decided to hide NULL metric units rather than showing it as "(null)",
but on hybrid systems if the process doesn't hit a PMU you get an empty
string metric unit instead. To make it consistent also remove empty
strings.

Note that metric-threshold is already hidden in this case without this
change.

Where a process only runs on cpu_core and never hits cpu_atom:
Before:
 $ perf stat -j -- true
 ...
 {"counter-value" : "<not counted>", "unit" : "", "event" : "cpu_atom/branch-misses/", "event-runtime" : 0, "pcnt-running" : 0.00, "metric-value" : "0.000000", "metric-unit" : ""}
 {"counter-value" : "6326.000000", "unit" : "", "event" : "cpu_core/branch-misses/", "event-runtime" : 293786, "pcnt-running" : 100.00, "metric-value" : "3.553394", "metric-unit" : "of all branches", "metric-threshold" : "good"}
 ...

After:
 ...
 {"counter-value" : "<not counted>", "unit" : "", "event" : "cpu_atom/branch-misses/", "event-runtime" : 0, "pcnt-running" : 0.00}
 {"counter-value" : "5778.000000", "unit" : "", "event" : "cpu_core/branch-misses/", "event-runtime" : 282240, "pcnt-running" : 100.00, "metric-value" : "3.226797", "metric-unit" : "of all branches", "metric-threshold" : "good"}
 ...

Signed-off-by: James Clark <james.clark@...aro.org>
---
 tools/perf/util/stat-display.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index a5d72f4a515c..9b7fd985a42a 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -506,7 +506,7 @@ static void print_metric_json(struct perf_stat_config *config __maybe_unused,
 	struct outstate *os = ctx;
 	FILE *out = os->fh;
 
-	if (unit) {
+	if (unit && strlen(unit)) {
 		json_out(os, "\"metric-value\" : \"%f\", \"metric-unit\" : \"%s\"", val, unit);
 		if (thresh != METRIC_THRESHOLD_UNKNOWN) {
 			json_out(os, "\"metric-threshold\" : \"%s\"",
-- 
2.34.1