perf data convert: Prefer sampled CPU when exporting JSON

When CPU has been explicitly sampled (via --sample-cpu), prefer this
sampled value over the thread CPU value when exporting to JSON.

Signed-off-by: Shawn M. Chapla <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/data-convert-json.c

···
 	struct convert_json *c = container_of(tool, struct convert_json, tool);
 	FILE *out = c->out;
 	struct addr_location al, tal;
+	u64 sample_type = __evlist__combined_sample_type(evsel->evlist);
 	u8 cpumode = PERF_RECORD_MISC_USER;
 
 	if (machine__resolve(machine, &al, sample) < 0) {
···
 	output_json_key_format(out, true, 3, "pid", "%i", al.thread->pid_);
 	output_json_key_format(out, true, 3, "tid", "%i", al.thread->tid);
 
-	if (al.thread->cpu >= 0)
+	if ((sample_type & PERF_SAMPLE_CPU))
+		output_json_key_format(out, true, 3, "cpu", "%i", sample->cpu);
+	else if (al.thread->cpu >= 0)
 		output_json_key_format(out, true, 3, "cpu", "%i", al.thread->cpu);
 
 	output_json_key_string(out, true, 3, "comm", thread__comm_str(al.thread));