Commit 628e1244 authored by Leo Yan's avatar Leo Yan Committed by Arnaldo Carvalho de Melo
Browse files

perf tests switch-tracking: Fix timestamp comparison 



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: d44bc558 ("perf tests: Add a test for tracking with sched_switch")
Reviewed-by: default avatarIan Rogers <irogers@google.com>
Signed-off-by: default avatarLeo 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 0ffca606

tools/perf/tests/switch-tracking.c

+1 −1
Original line number Diff line number Diff line
@@ -264,7 +264,7 @@ 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,