From: Leo Yan <leo.yan@arm.com>
Date: Mon, 31 Mar 2025 17:27:59 +0000 (+0100)
Subject: perf tests switch-tracking: Fix timestamp comparison
X-Git-Tag: v6.16-rc1~57^2~21
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=628e124404b3db5e10e17228e680a2999018ab33;p=thirdparty%2Flinux.git

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: 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>
---

diff --git a/tools/perf/tests/switch-tracking.c b/tools/perf/tests/switch-tracking.c
index 8df3f9d9ffd2b..6b3aac283c371 100644
--- a/tools/perf/tests/switch-tracking.c
+++ b/tools/perf/tests/switch-tracking.c
@@ -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,