[PATCH v2 2/2] perf stat: Also hide metric-units from JSON when event didn't run

[James Clark <james.clark@linaro.org>]

We decided to hide NULL metric-units rather than showing it as "(null)"
when a dependent event for a metric doesn't exist. But on hybrid systems
if the process doesn't hit a PMU you get an empty string metric unit
instead. To make it consistent change all empty strings to NULL.

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@linaro.org>
---
 tools/perf/util/stat-display.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index a5d72f4a515c..0e16eecfbad8 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -854,7 +854,8 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 
 	if (run == 0 || ena == 0 || counter->counts->scaled == -1) {
 		if (config->metric_only) {
-			pm(config, os, METRIC_THRESHOLD_UNKNOWN, "", "", 0);
+			pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL,
+			   /*unit=*/NULL, /*val=*/0);
 			return;
 		}
 
@@ -909,7 +910,7 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 			perf_stat__print_shadow_stats(config, counter, uval, aggr_idx,
 						      &out, &config->metric_events);
 	} else {
-		pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL, /*unit=*/"", /*val=*/0);
+		pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL, /*unit=*/NULL, /*val=*/0);
 	}
 
 	if (!config->metric_only) {
-- 
2.34.1