perf cpumap: More cpu map reuse by merge.

perf_cpu_map__merge() will reuse one of its arguments if they are equal or
the other argument is NULL.

The arguments could be reused if it is known one set of values is a
subset of the other.

For example, a map of 0-1 and a map of just 0 when merged yields the map
of 0-1.

Currently a new map is created rather than adding a reference count to
the original 0-1 map.

Signed-off-by: Ian Rogers <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Antonov <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Alexey Bayduraev <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Andrii Nakryiko <[e-mail]>
Cc: Daniel Borkmann <[e-mail]>
Cc: German Gomez <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: John Fastabend <[e-mail]>
Cc: John Garry <[e-mail]>
Cc: KP Singh <[e-mail]>
Cc: Kajol Jain <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Martin KaFai Lau <[e-mail]>
Cc: Mathieu Poirier <[e-mail]>
Cc: Mike Leach <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Riccardo Mancini <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Suzuki Poulouse <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Yonghong Song <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/perf/cpumap.c

···
 	int i, j, k;
 	struct perf_cpu_map *merged;
 
-	if (!orig && !other)
-		return NULL;
-	if (!orig) {
-		perf_cpu_map__get(other);
-		return other;
+	if (perf_cpu_map__is_subset(orig, other))
+		return orig;
+	if (perf_cpu_map__is_subset(other, orig)) {
+		perf_cpu_map__put(orig);
+		return perf_cpu_map__get(other);
 	}
-	if (!other)
-		return orig;
-	if (orig->nr == other->nr &&
-	    !memcmp(orig->map, other->map, orig->nr * sizeof(struct perf_cpu)))
-		return orig;
 
 	tmp_len = orig->nr + other->nr;
 	tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));