linux-kernel - [PATCH v4 7/7] perf/lib/cpumap: Warn when exceeding MAX_NR

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Date:   Tue, 27 Aug 2019 16:43:52 -0500
From:   Kyle Meyer <meyerk@....com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Kyle Meyer <meyerk@....com>, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org,
        Russ Anderson <russ.anderson@....com>,
        Kyle Meyer <kyle.meyer@....com>
Subject: [PATCH v4 7/7] perf/lib/cpumap: Warn when exceeding MAX_NR_CPUS

Display a warning when attempting to profile more than MAX_NR_CPU CPUs.
This patch should not change any behavior.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: linux-kernel@...r.kernel.org
Cc: Russ Anderson <russ.anderson@....com>
Signed-off-by: Kyle Meyer <kyle.meyer@....com>
---
 tools/perf/lib/cpumap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/lib/cpumap.c b/tools/perf/lib/cpumap.c
index 2834753576b2..1f0e6f334237 100644
--- a/tools/perf/lib/cpumap.c
+++ b/tools/perf/lib/cpumap.c
@@ -100,6 +100,9 @@ struct perf_cpu_map *perf_cpu_map__read(FILE *file)
 		if (prev >= 0) {
 			int new_max = nr_cpus + cpu - prev - 1;
 
+			WARN_ONCE(new_max >= MAX_NR_CPUS, "Perf can support %d CPUs. "
+							  "Consider raising MAX_NR_CPUS\n", MAX_NR_CPUS);
+
 			if (new_max >= max_entries) {
 				max_entries = new_max + MAX_NR_CPUS / 2;
 				tmp = realloc(tmp_cpus, max_entries * sizeof(int));
@@ -192,6 +195,9 @@ struct perf_cpu_map *perf_cpu_map__new(const char *cpu_list)
 			end_cpu = start_cpu;
 		}
 
+		WARN_ONCE(end_cpu >= MAX_NR_CPUS, "Perf can support %d CPUs. "
+						  "Consider raising MAX_NR_CPUS\n", MAX_NR_CPUS);
+
 		for (; start_cpu <= end_cpu; start_cpu++) {
 			/* check for duplicates */
 			for (i = 0; i < nr_cpus; i++)
-- 
2.12.3