6.6-stable review patch. If anyone has any objections, please let me know.
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From: Leo Yan leo.yan@arm.com
[ Upstream commit 628e124404b3db5e10e17228e680a2999018ab33 ]
The test might fail on the Arm64 platform with the error:
# perf test -vvv "Track with sched_switch" Missing sched_switch events #
The issue is caused by incorrect handling of timestamp comparisons. The comparison result, a signed 64-bit value, was being directly cast to an int, leading to incorrect sorting for sched events.
The case does not fail everytime, usually I can trigger the failure after run 20 ~ 30 times:
# while true; do perf test "Track with sched_switch"; done 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : FAILED! 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok 106: Track with sched_switch : FAILED! 106: Track with sched_switch : Ok 106: Track with sched_switch : Ok
I used cross compiler to build Perf tool on my host machine and tested on Debian / Juno board. Generally, I think this issue is not very specific to GCC versions. As both internal CI and my local env can reproduce the issue.
My Host Build compiler:
# aarch64-linux-gnu-gcc --version aarch64-linux-gnu-gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
Juno Board:
# lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 12 (bookworm) Release: 12 Codename: bookworm
Fix this by explicitly returning 0, 1, or -1 based on whether the result is zero, positive, or negative.
Fixes: d44bc558297222d9 ("perf tests: Add a test for tracking with sched_switch") Reviewed-by: Ian Rogers irogers@google.com Signed-off-by: Leo Yan leo.yan@arm.com Cc: Adrian Hunter adrian.hunter@intel.com Cc: James Clark james.clark@linaro.org Cc: Kan Liang kan.liang@linux.intel.com Cc: Namhyung Kim namhyung@kernel.org Link: https://lore.kernel.org/r/20250331172759.115604-1-leo.yan@arm.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/tests/switch-tracking.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/tests/switch-tracking.c b/tools/perf/tests/switch-tracking.c index e52b031bedc5a..2c7bdf4fd55ed 100644 --- a/tools/perf/tests/switch-tracking.c +++ b/tools/perf/tests/switch-tracking.c @@ -258,7 +258,7 @@ static int compar(const void *a, const void *b) const struct event_node *nodeb = b; s64 cmp = nodea->event_time - nodeb->event_time;
- return cmp; + return cmp < 0 ? -1 : (cmp > 0 ? 1 : 0); }
static int process_events(struct evlist *evlist,