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Subject[PATCH v2] perf evlist: Avoid iteration for empty evlist.
From
As seen with 'perf stat --null ..' and reported in:
https://lore.kernel.org/lkml/YjCLcpcX2peeQVCH@kernel.org/

v2. Avoids setting evsel in the empty list case as suggested by Jiri
Olsa <jolsa@kernel.org>.
Fixes: 472832d2c000 ("perf evlist: Refactor evlist__for_each_cpu()")
Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/evlist.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 8134d45e2164..9bb79e049957 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -346,7 +346,7 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
{
struct evlist_cpu_iterator itr = {
.container = evlist,
- .evsel = evlist__first(evlist),
+ .evsel = NULL,
.cpu_map_idx = 0,
.evlist_cpu_map_idx = 0,
.evlist_cpu_map_nr = perf_cpu_map__nr(evlist->core.all_cpus),
@@ -354,16 +354,22 @@ struct evlist_cpu_iterator evlist__cpu_begin(struct evlist *evlist, struct affin
.affinity = affinity,
};

- 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);
- /*
- * If this CPU isn't in the evsel's cpu map then advance through
- * the list.
- */
- if (itr.cpu_map_idx == -1)
- evlist_cpu_iterator__next(&itr);
+ if (evlist__empty(evlist)) {
+ /* Ensure the empty list doesn't iterate. */
+ itr.evlist_cpu_map_idx = itr.evlist_cpu_map_nr;
+ } else {
+ itr.evsel = evlist__first(evlist);
+ 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);
+ /*
+ * If this CPU isn't in the evsel's cpu map then advance
+ * through the list.
+ */
+ if (itr.cpu_map_idx == -1)
+ evlist_cpu_iterator__next(&itr);
+ }
}
return itr;
}
--
2.35.1.894.gb6a874cedc-goog
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