perf stat: Add JSON output option

CSV output is tricky to format and column layout changes are susceptible
to breaking parsers. New JSON-formatted output has variable names to
identify fields that are consistent and informative, making the output
parseable.

CSV output example:

  1.20,msec,task-clock:u,1204272,100.00,0.697,CPUs utilized
  0,,context-switches:u,1204272,100.00,0.000,/sec
  0,,cpu-migrations:u,1204272,100.00,0.000,/sec
  70,,page-faults:u,1204272,100.00,58.126,K/sec

JSON output example:

  {"counter-value" : "3805.723968", "unit" : "msec", "event" :
  "cpu-clock", "event-runtime" : 3805731510100.00, "pcnt-running"
  : 100.00, "metric-value" : 4.007571, "metric-unit" : "CPUs utilized"}
  {"counter-value" : "6166.000000", "unit" : "", "event" :
  "context-switches", "event-runtime" : 3805723045100.00, "pcnt-running"
  : 100.00, "metric-value" : 1.620191, "metric-unit" : "K/sec"}
  {"counter-value" : "466.000000", "unit" : "", "event" :
  "cpu-migrations", "event-runtime" : 3805727613100.00, "pcnt-running"
  : 100.00, "metric-value" : 122.447136, "metric-unit" : "/sec"}
  {"counter-value" : "208.000000", "unit" : "", "event" :
  "page-faults", "event-runtime" : 3805726799100.00, "pcnt-running"
  : 100.00, "metric-value" : 54.654516, "metric-unit" : "/sec"}

Also added documentation for JSON option.

There is some tidy up of CSV code including a potential memory over run
in the os.nfields set up. To facilitate this an AGGR_MAX value is added.

Committer notes:

Fixed up using PRIu64 to format u64 values, not %lu.

Committer testing:

  ⬢[acme@toolbox perf]$ perf stat -j sleep 1
  {"counter-value" : "0.731750", "unit" : "msec", "event" : "task-clock:u", "event-runtime" : 731750, "pcnt-running" : 100.00, "metric-value" : 0.000731, "metric-unit" : "CPUs utilized"}
  {"counter-value" : "0.000000", "unit" : "", "event" : "context-switches:u", "event-runtime" : 731750, "pcnt-running" : 100.00, "metric-value" : 0.000000, "metric-unit" : "/sec"}
  {"counter-value" : "0.000000", "unit" : "", "event" : "cpu-migrations:u", "event-runtime" : 731750, "pcnt-running" : 100.00, "metric-value" : 0.000000, "metric-unit" : "/sec"}
  {"counter-value" : "75.000000", "unit" : "", "event" : "page-faults:u", "event-runtime" : 731750, "pcnt-running" : 100.00, "metric-value" : 102.494021, "metric-unit" : "K/sec"}
  {"counter-value" : "578765.000000", "unit" : "", "event" : "cycles:u", "event-runtime" : 379366, "pcnt-running" : 49.00, "metric-value" : 0.790933, "metric-unit" : "GHz"}
  {"counter-value" : "1298.000000", "unit" : "", "event" : "stalled-cycles-frontend:u", "event-runtime" : 768020, "pcnt-running" : 100.00, "metric-value" : 0.224271, "metric-unit" : "frontend cycles idle"}
  {"counter-value" : "21984.000000", "unit" : "", "event" : "stalled-cycles-backend:u", "event-runtime" : 768020, "pcnt-running" : 100.00, "metric-value" : 3.798433, "metric-unit" : "backend cycles idle"}
  {"counter-value" : "468197.000000", "unit" : "", "event" : "instructions:u", "event-runtime" : 768020, "pcnt-running" : 100.00, "metric-value" : 0.808959, "metric-unit" : "insn per cycle"}
  {"metric-value" : 0.046955, "metric-unit" : "stalled cycles per insn"}
  {"counter-value" : "103335.000000", "unit" : "", "event" : "branches:u", "event-runtime" : 768020, "pcnt-running" : 100.00, "metric-value" : 141.216262, "metric-unit" : "M/sec"}
  {"counter-value" : "2381.000000", "unit" : "", "event" : "branch-misses:u", "event-runtime" : 388654, "pcnt-running" : 50.00, "metric-value" : 2.304156, "metric-unit" : "of all branches"}
  ⬢[acme@toolbox perf]$

Signed-off-by: Claire Jensen <cjense@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alyssa Ross <hi@alyssa.is>
Cc: Claire Jensen <clairej735@gmail.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Like Xu <likexu@tencent.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20220805200105.2020995-2-irogers@google.com
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

5 files changed, 307 insertions, 106 deletions

diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index d8a33f4a47c5..d7ff1867feda 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -570,6 +570,27 @@ Additional metrics may be printed with all earlier fields being empty.
 
 include::intel-hybrid.txt[]
 
+JSON FORMAT
+-----------
+
+With -j, perf stat is able to print out a JSON format output
+that can be used for parsing.
+
+- timestamp : optional usec time stamp in fractions of second (with -I)
+- optional aggregate options:
+		- core : core identifier (with --per-core)
+		- die : die identifier (with --per-die)
+		- socket : socket identifier (with --per-socket)
+		- node : node identifier (with --per-node)
+		- thread : thread identifier (with --per-thread)
+- counter-value : counter value
+- unit : unit of the counter value or empty
+- event : event name
+- variance : optional variance if multiple values are collected (with -r)
+- runtime : run time of counter
+- metric-value : optional metric value
+- metric-unit : optional unit of metric
+
 SEE ALSO
 --------
 linkperf:perf-top[1], linkperf:perf-list[1]
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index b5ce07c5738a..0d9fec377071 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -1250,6 +1250,8 @@ static struct option stat_options[] = {
 		    "Merge identical named hybrid events"),
 	OPT_STRING('x', "field-separator", &stat_config.csv_sep, "separator",
 		   "print counts with custom separator"),
+	OPT_BOOLEAN('j', "json-output", &stat_config.json_output,
+		   "print counts in JSON format"),
 	OPT_CALLBACK('G', "cgroup", &evsel_list, "name",
 		     "monitor event in cgroup name only", parse_stat_cgroups),
 	OPT_STRING(0, "for-each-cgroup", &stat_config.cgroup_list, "name",
@@ -1436,6 +1438,7 @@ static aggr_cpu_id_get_t aggr_mode__get_aggr(enum aggr_mode aggr_mode)
 	case AGGR_GLOBAL:
 	case AGGR_THREAD:
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		return NULL;
 	}
@@ -1460,6 +1463,7 @@ static aggr_get_id_t aggr_mode__get_id(enum aggr_mode aggr_mode)
 	case AGGR_GLOBAL:
 	case AGGR_THREAD:
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		return NULL;
 	}
@@ -1610,6 +1614,7 @@ static aggr_cpu_id_get_t aggr_mode__get_aggr_file(enum aggr_mode aggr_mode)
 	case AGGR_GLOBAL:
 	case AGGR_THREAD:
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		return NULL;
 	}
@@ -1630,6 +1635,7 @@ static aggr_get_id_t aggr_mode__get_id_file(enum aggr_mode aggr_mode)
 	case AGGR_GLOBAL:
 	case AGGR_THREAD:
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		return NULL;
 	}
diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index 44045565c8f8..b82844cb0ce7 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -28,15 +28,21 @@
 static void print_running(struct perf_stat_config *config,
 			  u64 run, u64 ena)
 {
-	if (config->csv_output) {
-		fprintf(config->output, "%s%" PRIu64 "%s%.2f",
-					config->csv_sep,
-					run,
-					config->csv_sep,
-					ena ? 100.0 * run / ena : 100.0);
-	} else if (run != ena) {
+
+	double enabled_percent = 100;
+
+	if (run != ena)
+		enabled_percent = 100 * run / ena;
+	if (config->json_output)
+		fprintf(config->output,
+			"\"event-runtime\" : %" PRIu64 ", \"pcnt-running\" : %.2f, ",
+			run, enabled_percent);
+	else if (config->csv_output)
+		fprintf(config->output,
+			"%s%" PRIu64 "%s%.2f", config->csv_sep,
+			run, config->csv_sep, enabled_percent);
+	else if (run != ena)
 		fprintf(config->output, "  (%.2f%%)", 100.0 * run / ena);
-	}
 }
 
 static void print_noise_pct(struct perf_stat_config *config,
@@ -44,7 +50,9 @@ static void print_noise_pct(struct perf_stat_config *config,
 {
 	double pct = rel_stddev_stats(total, avg);
 
-	if (config->csv_output)
+	if (config->json_output)
+		fprintf(config->output, "\"variance\" : %.2f, ", pct);
+	else if (config->csv_output)
 		fprintf(config->output, "%s%.2f%%", config->csv_sep, pct);
 	else if (pct)
 		fprintf(config->output, "  ( +-%6.2f%% )", pct);
@@ -66,7 +74,11 @@ static void print_cgroup(struct perf_stat_config *config, struct evsel *evsel)
 {
 	if (nr_cgroups) {
 		const char *cgrp_name = evsel->cgrp ? evsel->cgrp->name  : "";
-		fprintf(config->output, "%s%s", config->csv_sep, cgrp_name);
+
+		if (config->json_output)
+			fprintf(config->output, "\"cgroup\" : \"%s\", ", cgrp_name);
+		else
+			fprintf(config->output, "%s%s", config->csv_sep, cgrp_name);
 	}
 }
 
@@ -74,69 +86,123 @@ static void print_cgroup(struct perf_stat_config *config, struct evsel *evsel)
 static void aggr_printout(struct perf_stat_config *config,
 			  struct evsel *evsel, struct aggr_cpu_id id, int nr)
 {
+
+
+	if (config->json_output && !config->interval)
+		fprintf(config->output, "{");
+
 	switch (config->aggr_mode) {
 	case AGGR_CORE:
-		fprintf(config->output, "S%d-D%d-C%*d%s%*d%s",
-			id.socket,
-			id.die,
-			config->csv_output ? 0 : -8,
-			id.core,
-			config->csv_sep,
-			config->csv_output ? 0 : 4,
-			nr,
-			config->csv_sep);
+		if (config->json_output) {
+			fprintf(config->output,
+				"\"core\" : \"S%d-D%d-C%d\", \"aggregate-number\" : %d, ",
+				id.socket,
+				id.die,
+				id.core,
+				nr);
+		} else {
+			fprintf(config->output, "S%d-D%d-C%*d%s%*d%s",
+				id.socket,
+				id.die,
+				config->csv_output ? 0 : -8,
+				id.core,
+				config->csv_sep,
+				config->csv_output ? 0 : 4,
+				nr,
+				config->csv_sep);
+		}
 		break;
 	case AGGR_DIE:
-		fprintf(config->output, "S%d-D%*d%s%*d%s",
-			id.socket,
-			config->csv_output ? 0 : -8,
-			id.die,
-			config->csv_sep,
-			config->csv_output ? 0 : 4,
-			nr,
-			config->csv_sep);
+		if (config->json_output) {
+			fprintf(config->output,
+				"\"die\" : \"S%d-D%d\", \"aggregate-number\" : %d, ",
+				id.socket,
+				id.die,
+				nr);
+		} else {
+			fprintf(config->output, "S%d-D%*d%s%*d%s",
+				id.socket,
+				config->csv_output ? 0 : -8,
+				id.die,
+				config->csv_sep,
+				config->csv_output ? 0 : 4,
+				nr,
+				config->csv_sep);
+		}
 		break;
 	case AGGR_SOCKET:
-		fprintf(config->output, "S%*d%s%*d%s",
-			config->csv_output ? 0 : -5,
-			id.socket,
-			config->csv_sep,
-			config->csv_output ? 0 : 4,
-			nr,
-			config->csv_sep);
-			break;
+		if (config->json_output) {
+			fprintf(config->output,
+				"\"socket\" : \"S%d\", \"aggregate-number\" : %d, ",
+				id.socket,
+				nr);
+		} else {
+			fprintf(config->output, "S%*d%s%*d%s",
+				config->csv_output ? 0 : -5,
+				id.socket,
+				config->csv_sep,
+				config->csv_output ? 0 : 4,
+				nr,
+				config->csv_sep);
+		}
+		break;
 	case AGGR_NODE:
-		fprintf(config->output, "N%*d%s%*d%s",
-			config->csv_output ? 0 : -5,
-			id.node,
-			config->csv_sep,
-			config->csv_output ? 0 : 4,
-			nr,
-			config->csv_sep);
-			break;
+		if (config->json_output) {
+			fprintf(config->output, "\"node\" : \"N%d\", \"aggregate-number\" : %d, ",
+				id.node,
+				nr);
+		} else {
+			fprintf(config->output, "N%*d%s%*d%s",
+				config->csv_output ? 0 : -5,
+				id.node,
+				config->csv_sep,
+				config->csv_output ? 0 : 4,
+				nr,
+				config->csv_sep);
+		}
+		break;
 	case AGGR_NONE:
-		if (evsel->percore && !config->percore_show_thread) {
-			fprintf(config->output, "S%d-D%d-C%*d%s",
-				id.socket,
-				id.die,
-				config->csv_output ? 0 : -3,
-				id.core, config->csv_sep);
-		} else if (id.cpu.cpu > -1) {
-			fprintf(config->output, "CPU%*d%s",
-				config->csv_output ? 0 : -7,
-				id.cpu.cpu, config->csv_sep);
+		if (config->json_output) {
+			if (evsel->percore && !config->percore_show_thread) {
+				fprintf(config->output, "\"core\" : \"S%d-D%d-C%d\"",
+					id.socket,
+					id.die,
+					id.core);
+			} else if (id.core > -1) {
+				fprintf(config->output, "\"cpu\" : \"%d\", ",
+					id.cpu.cpu);
+			}
+		} else {
+			if (evsel->percore && !config->percore_show_thread) {
+				fprintf(config->output, "S%d-D%d-C%*d%s",
+					id.socket,
+					id.die,
+					config->csv_output ? 0 : -3,
+					id.core, config->csv_sep);
+			} else if (id.core > -1) {
+				fprintf(config->output, "CPU%*d%s",
+					config->csv_output ? 0 : -7,
+					id.cpu.cpu, config->csv_sep);
+			}
 		}
 		break;
 	case AGGR_THREAD:
-		fprintf(config->output, "%*s-%*d%s",
-			config->csv_output ? 0 : 16,
-			perf_thread_map__comm(evsel->core.threads, id.thread),
-			config->csv_output ? 0 : -8,
-			perf_thread_map__pid(evsel->core.threads, id.thread),
-			config->csv_sep);
+		if (config->json_output) {
+			fprintf(config->output, "\"thread\" : \"%s-%d\", ",
+				perf_thread_map__comm(evsel->core.threads, id.thread),
+				perf_thread_map__pid(evsel->core.threads, id.thread));
+		} else {
+			fprintf(config->output, "%*s-%*d%s",
+				config->csv_output ? 0 : 16,
+				perf_thread_map__comm(evsel->core.threads, id.thread),
+				config->csv_output ? 0 : -8,
+				perf_thread_map__pid(evsel->core.threads, id.thread),
+				config->csv_sep);
+		}
 		break;
 	case AGGR_GLOBAL:
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		break;
 	}
@@ -234,6 +300,31 @@ static void print_metric_csv(struct perf_stat_config *config __maybe_unused,
 	fprintf(out, "%s%s%s%s", config->csv_sep, vals, config->csv_sep, skip_spaces(unit));
 }
 
+static void print_metric_json(struct perf_stat_config *config __maybe_unused,
+			     void *ctx,
+			     const char *color __maybe_unused,
+			     const char *fmt __maybe_unused,
+			     const char *unit, double val)
+{
+	struct outstate *os = ctx;
+	FILE *out = os->fh;
+
+	fprintf(out, "\"metric-value\" : %f, ", val);
+	fprintf(out, "\"metric-unit\" : \"%s\"", unit);
+	if (!config->metric_only)
+		fprintf(out, "}");
+}
+
+static void new_line_json(struct perf_stat_config *config, void *ctx)
+{
+	struct outstate *os = ctx;
+
+	fputc('\n', os->fh);
+	if (os->prefix)
+		fprintf(os->fh, "%s", os->prefix);
+	aggr_printout(config, os->evsel, os->id, os->nr);
+}
+
 /* Filter out some columns that don't work well in metrics only mode */
 
 static bool valid_only_metric(const char *unit)
@@ -300,6 +391,27 @@ static void print_metric_only_csv(struct perf_stat_config *config __maybe_unused
 	fprintf(out, "%s%s", vals, config->csv_sep);
 }
 
+static void print_metric_only_json(struct perf_stat_config *config __maybe_unused,
+				  void *ctx, const char *color __maybe_unused,
+				  const char *fmt,
+				  const char *unit, double val)
+{
+	struct outstate *os = ctx;
+	FILE *out = os->fh;
+	char buf[64], *vals, *ends;
+	char tbuf[1024];
+
+	if (!valid_only_metric(unit))
+		return;
+	unit = fixunit(tbuf, os->evsel, unit);
+	snprintf(buf, sizeof(buf), fmt, val);
+	ends = vals = skip_spaces(buf);
+	while (isdigit(*ends) || *ends == '.')
+		ends++;
+	*ends = 0;
+	fprintf(out, "{\"metric-value\" : \"%s\"}", vals);
+}
+
 static void new_line_metric(struct perf_stat_config *config __maybe_unused,
 			    void *ctx __maybe_unused)
 {
@@ -318,10 +430,13 @@ static void print_metric_header(struct perf_stat_config *config,
 	    os->evsel->priv != os->evsel->evlist->selected->priv)
 		return;
 
-	if (!valid_only_metric(unit))
+	if (!valid_only_metric(unit) && !config->json_output)
 		return;
 	unit = fixunit(tbuf, os->evsel, unit);
-	if (config->csv_output)
+
+	if (config->json_output)
+		fprintf(os->fh, "\"unit\" : \"%s\"", unit);
+	else if (config->csv_output)
 		fprintf(os->fh, "%s%s", unit, config->csv_sep);
 	else
 		fprintf(os->fh, "%*s ", config->metric_only_len, unit);
@@ -367,14 +482,27 @@ static void abs_printout(struct perf_stat_config *config,
 
 	aggr_printout(config, evsel, id, nr);
 
-	fprintf(output, fmt, avg, config->csv_sep);
+	if (config->json_output)
+		fprintf(output, "\"counter-value\" : \"%f\", ", avg);
+	else
+		fprintf(output, fmt, avg, config->csv_sep);
 
-	if (evsel->unit)
-		fprintf(output, "%-*s%s",
-			config->csv_output ? 0 : config->unit_width,
-			evsel->unit, config->csv_sep);
+	if (config->json_output) {
+		if (evsel->unit) {
+			fprintf(output, "\"unit\" : \"%s\", ",
+				evsel->unit);
+		}
+	} else {
+		if (evsel->unit)
+			fprintf(output, "%-*s%s",
+				config->csv_output ? 0 : config->unit_width,
+				evsel->unit, config->csv_sep);
+	}
 
-	fprintf(output, "%-*s", config->csv_output ? 0 : 32, evsel__name(evsel));
+	if (config->json_output)
+		fprintf(output, "\"event\" : \"%s\", ", evsel__name(evsel));
+	else
+		fprintf(output, "%-*s", config->csv_output ? 0 : 32, evsel__name(evsel));
 
 	print_cgroup(config, evsel);
 }
@@ -416,34 +544,30 @@ static void printout(struct perf_stat_config *config, struct aggr_cpu_id id, int
 		.nr = nr,
 		.evsel = counter,
 	};
-	print_metric_t pm = print_metric_std;
+	print_metric_t pm;
 	new_line_t nl;
 
-	if (config->metric_only) {
-		nl = new_line_metric;
-		if (config->csv_output)
-			pm = print_metric_only_csv;
-		else
-			pm = print_metric_only;
-	} else
-		nl = new_line_std;
-
-	if (config->csv_output && !config->metric_only) {
-		static int aggr_fields[] = {
-			[AGGR_GLOBAL] = 0,
-			[AGGR_THREAD] = 1,
+	if (config->csv_output) {
+		static const int aggr_fields[AGGR_MAX] = {
 			[AGGR_NONE] = 1,
+			[AGGR_GLOBAL] = 0,
 			[AGGR_SOCKET] = 2,
 			[AGGR_DIE] = 2,
 			[AGGR_CORE] = 2,
+			[AGGR_THREAD] = 1,
+			[AGGR_UNSET] = 0,
+			[AGGR_NODE] = 0,
 		};
 
-		pm = print_metric_csv;
-		nl = new_line_csv;
-		os.nfields = 3;
-		os.nfields += aggr_fields[config->aggr_mode];
-		if (counter->cgrp)
-			os.nfields++;
+		pm = config->metric_only ? print_metric_only_csv : print_metric_csv;
+		nl = config->metric_only ? new_line_metric : new_line_csv;
+		os.nfields = 3 + aggr_fields[config->aggr_mode] + (counter->cgrp ? 1 : 0);
+	} else if (config->json_output) {
+		pm = config->metric_only ? print_metric_only_json : print_metric_json;
+		nl = config->metric_only ? new_line_metric : new_line_json;
+	} else {
+		pm = config->metric_only ? print_metric_only : print_metric_std;
+		nl = config->metric_only ? new_line_metric : new_line_std;
 	}
 
 	if (!config->no_csv_summary && config->csv_output &&
@@ -458,10 +582,15 @@ static void printout(struct perf_stat_config *config, struct aggr_cpu_id id, int
 		}
 		aggr_printout(config, counter, id, nr);
 
-		fprintf(config->output, "%*s%s",
-			config->csv_output ? 0 : 18,
-			counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,
-			config->csv_sep);
+		if (config->json_output) {
+			fprintf(config->output, "\"counter-value\" : \"%s\", ",
+					counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED);
+		} else {
+			fprintf(config->output, "%*s%s",
+				config->csv_output ? 0 : 18,
+				counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,
+				config->csv_sep);
+		}
 
 		if (counter->supported) {
 			if (!evlist__has_hybrid(counter->evlist)) {
@@ -471,21 +600,32 @@ static void printout(struct perf_stat_config *config, struct aggr_cpu_id id, int
 			}
 		}
 
-		fprintf(config->output, "%-*s%s",
-			config->csv_output ? 0 : config->unit_width,
-			counter->unit, config->csv_sep);
+		if (config->json_output) {
+			fprintf(config->output, "\"unit\" : \"%s\", ", counter->unit);
+		} else {
+			fprintf(config->output, "%-*s%s",
+				config->csv_output ? 0 : config->unit_width,
+				counter->unit, config->csv_sep);
+		}
 
-		fprintf(config->output, "%*s",
-			config->csv_output ? 0 : -25, evsel__name(counter));
+		if (config->json_output) {
+			fprintf(config->output, "\"event\" : \"%s\", ",
+				evsel__name(counter));
+		} else {
+			fprintf(config->output, "%*s",
+				 config->csv_output ? 0 : -25, evsel__name(counter));
+		}
 
 		print_cgroup(config, counter);
 
-		if (!config->csv_output)
+		if (!config->csv_output && !config->json_output)
 			pm(config, &os, NULL, NULL, "", 0);
 		print_noise(config, counter, noise);
 		print_running(config, run, ena);
 		if (config->csv_output)
 			pm(config, &os, NULL, NULL, "", 0);
+		else if (config->json_output)
+			pm(config, &os, NULL, NULL, "", 0);
 		return;
 	}
 
@@ -500,12 +640,15 @@ static void printout(struct perf_stat_config *config, struct aggr_cpu_id id, int
 	if (config->csv_output && !config->metric_only) {
 		print_noise(config, counter, noise);
 		print_running(config, run, ena);
+	} else if (config->json_output && !config->metric_only) {
+		print_noise(config, counter, noise);
+		print_running(config, run, ena);
 	}
 
 	perf_stat__print_shadow_stats(config, counter, uval,
 				first_shadow_cpu_map_idx(config, counter, &id),
 				&out, &config->metric_events, st);
-	if (!config->csv_output && !config->metric_only) {
+	if (!config->csv_output && !config->metric_only && !config->json_output) {
 		print_noise(config, counter, noise);
 		print_running(config, run, ena);
 	}
@@ -1004,8 +1147,12 @@ static void print_metric_headers(struct perf_stat_config *config,
 	struct outstate os = {
 		.fh = config->output
 	};
+	bool first = true;
+
+		if (config->json_output && !config->interval)
+			fprintf(config->output, "{");
 
-	if (prefix)
+	if (prefix && !config->json_output)
 		fprintf(config->output, "%s", prefix);
 
 	if (!config->csv_output && !no_indent)
@@ -1025,6 +1172,9 @@ static void print_metric_headers(struct perf_stat_config *config,
 		os.evsel = counter;
 		out.ctx = &os;
 		out.print_metric = print_metric_header;
+		if (!first && config->json_output)
+			fprintf(config->output, ", ");
+		first = false;
 		out.new_line = new_line_metric;
 		out.force_header = true;
 		perf_stat__print_shadow_stats(config, counter, 0,
@@ -1033,6 +1183,8 @@ static void print_metric_headers(struct perf_stat_config *config,
 					      &config->metric_events,
 					      &rt_stat);
 	}
+	if (config->json_output)
+		fprintf(config->output, "}");
 	fputc('\n', config->output);
 }
 
@@ -1048,10 +1200,18 @@ static void print_interval(struct perf_stat_config *config,
 	if (config->interval_clear)
 		puts(CONSOLE_CLEAR);
 
-	if (!config->iostat_run)
-		sprintf(prefix, "%6lu.%09lu%s", (unsigned long) ts->tv_sec, ts->tv_nsec, config->csv_sep);
-
-	if ((num_print_interval == 0 && !config->csv_output) || config->interval_clear) {
+	if (!config->iostat_run && !config->json_output)
+		sprintf(prefix, "%6lu.%09lu%s", (unsigned long) ts->tv_sec,
+				 ts->tv_nsec, config->csv_sep);
+	if (!config->iostat_run && config->json_output && !config->metric_only)
+		sprintf(prefix, "{\"interval\" : %lu.%09lu, ", (unsigned long)
+				 ts->tv_sec, ts->tv_nsec);
+	if (!config->iostat_run && config->json_output && config->metric_only)
+		sprintf(prefix, "{\"interval\" : %lu.%09lu}", (unsigned long)
+				 ts->tv_sec, ts->tv_nsec);
+
+	if ((num_print_interval == 0 && !config->csv_output && !config->json_output)
+			 || config->interval_clear) {
 		switch (config->aggr_mode) {
 		case AGGR_NODE:
 			fprintf(output, "#           time node   cpus");
@@ -1091,12 +1251,19 @@ static void print_interval(struct perf_stat_config *config,
 					fprintf(output, "             counts %*s events\n", unit_width, "unit");
 			}
 		case AGGR_UNSET:
+		case AGGR_MAX:
 			break;
 		}
 	}
 
-	if ((num_print_interval == 0 || config->interval_clear) && metric_only)
+	if ((num_print_interval == 0 || config->interval_clear)
+			 && metric_only && !config->json_output)
 		print_metric_headers(config, evlist, " ", true);
+	if ((num_print_interval == 0 || config->interval_clear)
+			 && metric_only && config->json_output) {
+		fprintf(output, "{");
+		print_metric_headers(config, evlist, " ", true);
+	}
 	if (++num_print_interval == 25)
 		num_print_interval = 0;
 }
@@ -1110,7 +1277,7 @@ static void print_header(struct perf_stat_config *config,
 
 	fflush(stdout);
 
-	if (!config->csv_output) {
+	if (!config->csv_output && !config->json_output) {
 		fprintf(output, "\n");
 		fprintf(output, " Performance counter stats for ");
 		if (_target->bpf_str)
@@ -1303,6 +1470,9 @@ void evlist__print_counters(struct evlist *evlist, struct perf_stat_config *conf
 			num_print_iv = 0;
 		if (config->aggr_mode == AGGR_GLOBAL && prefix && !config->iostat_run)
 			fprintf(config->output, "%s", prefix);
+
+		if (config->json_output && !config->metric_only)
+			fprintf(config->output, "}");
 	}
 
 	switch (config->aggr_mode) {
@@ -1341,12 +1511,13 @@ void evlist__print_counters(struct evlist *evlist, struct perf_stat_config *conf
 			}
 		}
 		break;
+	case AGGR_MAX:
 	case AGGR_UNSET:
 	default:
 		break;
 	}
 
-	if (!interval && !config->csv_output)
+	if (!interval && !config->csv_output && !config->json_output)
 		print_footer(config);
 
 	fflush(config->output);
diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
index 37ea2d044708..0882b4754fcf 100644
--- a/tools/perf/util/stat.c
+++ b/tools/perf/util/stat.c
@@ -401,6 +401,7 @@ process_counter_values(struct perf_stat_config *config, struct evsel *evsel,
 		aggr->ena += count->ena;
 		aggr->run += count->run;
 	case AGGR_UNSET:
+	case AGGR_MAX:
 	default:
 		break;
 	}
diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
index b5aeb8e6d34b..668250022f8c 100644
--- a/tools/perf/util/stat.h
+++ b/tools/perf/util/stat.h
@@ -57,6 +57,7 @@ enum aggr_mode {
 	AGGR_THREAD,
 	AGGR_UNSET,
 	AGGR_NODE,
+	AGGR_MAX
 };
 
 enum {
@@ -121,6 +122,7 @@ struct perf_stat_config {
 	bool			 no_inherit;
 	bool			 identifier;
 	bool			 csv_output;
+	bool			 json_output;
 	bool			 interval_clear;
 	bool			 metric_only;
 	bool			 null_run;