linux-kernel - [PATCH] perf evlist: Avoid iteration for empty evlist.

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Date:   Wed, 16 Mar 2022 00:10:49 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Ian Rogers <irogers@...gle.com>
Subject: [PATCH] perf evlist: Avoid iteration for empty evlist.

As seen with 'perf stat --null ..' and reported in:
https://lore.kernel.org/lkml/YjCLcpcX2peeQVCH@kernel.org/

Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()")
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/evlist.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 8134d45e2164..a2dba9e00765 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -354,7 +354,10 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
 		.affinity = affinity,
 	};
 
-	if (itr.affinity) {
+	if (evlist__empty(evlist)) {
+		/* Ensure the empty list doesn't iterate. */
+		itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
+	} else if (itr.affinity) {
 		itr.cpu = perf_cpu_map__cpu(evlist->core.all_cpus, 0);
 		affinity__set(itr.affinity, itr.cpu.cpu);
 		itr.cpu_map_idx = perf_cpu_map__idx(itr.evsel->core.cpus, itr.cpu);
-- 
2.35.1.723.g4982287a31-goog