libperf cpumap: Use binary search in perf_cpu_map__idx() as array are sorted

Since 7074674e ("perf cpumap: Maintain cpumaps ordered and
without dups") perf_cpu_map elements are sorted in ascending order.

This patch improves perf_cpu_map__idx() by using a binary search.
Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/f1543c15797169c21e8b205a4a6751159180580d.1629490974.git.rickyman7@gmail.com
[ Removed 'else' after if + return, declared variables where needed ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/cpumap.c

@@ -270,11 +270,19 @@ bool perf_cpu_map__empty(const struct perf_cpu_map *map)
 
 int perf_cpu_map__idx(struct perf_cpu_map *cpus, int cpu)
 {
-	int i;
+	int low = 0, high = cpus->nr;
 
-	for (i = 0; i < cpus->nr; ++i) {
-		if (cpus->map[i] == cpu)
-			return i;
+	while (low < high) {
+		int idx = (low + high) / 2,
+		    cpu_at_idx = cpus->map[idx];
+
+		if (cpu_at_idx == cpu)
+			return idx;
+
+		if (cpu_at_idx > cpu)
+			high = idx;
+		else
+			low = idx + 1;
 	}
 
 	return -1;