linux-kernel - [RFC PATCH v1 01/37] libperf cpumap: improve idx function

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Date:   Sat, 21 Aug 2021 11:19:07 +0200
From:   Riccardo Mancini <rickyman7@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Riccardo Mancini <rickyman7@...il.com>
Subject: [RFC PATCH v1 01/37] libperf cpumap: improve idx function

>From commit 7074674e7338863e ("perf cpumap: Maintain cpumaps ordered
and without dups"), perf_cpu_map elements are sorted in ascending order.

This patch improves the perf_cpu_map__idx function by using a binary
search.

Signed-off-by: Riccardo Mancini <rickyman7@...il.com>
---
 tools/lib/perf/cpumap.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index ca0215047c326af4..fb633272be3aaed9 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -265,11 +265,18 @@ 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, idx, cpu_at_idx;
 
-	for (i = 0; i < cpus->nr; ++i) {
-		if (cpus->map[i] == cpu)
-			return i;
+	while (low < high) {
+		idx = (low + high) / 2;
+		cpu_at_idx = cpus->map[idx];
+
+		if (cpu_at_idx == cpu)
+			return idx;
+		else if (cpu_at_idx > cpu)
+			high = idx;
+		else
+			low = idx+1;
 	}
 
 	return -1;
-- 
2.31.1