[tip: timers/core] selftests: timers: Measure the CPU timers on the clock they count

[tip-bot2 for Eva Kurchatova]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     b03638013add0609d35aaa8291548dea92cb9484
Gitweb:        https://git.kernel.org/tip/b03638013add0609d35aaa8291548dea92cb9484
Author:        Eva Kurchatova <eva.kurchatova@xxxxxxxxxxxxx>
AuthorDate:    Thu, 17 Sep 2026 04:52:32 +03:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Tue, 29 Sep 2026 22:03:31 +02:00

selftests: timers: Measure the CPU timers on the clock they count

Commit b00385b8d081 ("selftests/posix_timers: Use CLOCK_THREAD_CPUTIME_ID
for ITIMER_PROF measurements") gave ITIMER_PROF the clock it counts, as
measuring a CPU timer against the wall says nothing on a machine where
the task does not have a CPU to itself. The other CPU timers are still
measured against CLOCK_REALTIME and fail the same way. With four busy
loops on the two CPUs of a test machine:

  not ok 2 ITIMER_VIRTUAL
  not ok 5 timer_create() per CLOCK_THREAD_CPUTIME_ID
  not ok 6 timer_create() per CLOCK_PROCESS_CPUTIME_ID

ITIMER_VIRTUAL counts the time the task spends in userspace, so take
CLOCK_THREAD_CPUTIME_ID for it as well; the loop it runs stays in
userspace, so what that clock adds for system time is far inside the
half a second the check allows. check_timer_create() arms its timer on
the clock it is given, so measure on that one.

The test then passes whole on that machine, 19 of 19, busy or idle.

Signed-off-by: Eva Kurchatova <eva.kurchatova@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Acked-by: John Stultz <jstultz@xxxxxxxxxx>
Link: https://patch.msgid.link/20260917015237.2462954-2-eva.kurchatova@xxxxxxxxxxxxx
---
 tools/testing/selftests/timers/posix_timers.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c
index a92d4b9..52b7289 100644
--- a/tools/testing/selftests/timers/posix_timers.c
+++ b/tools/testing/selftests/timers/posix_timers.c
@@ -113,9 +113,10 @@ static void check_itimer(int which, const char *name)
 
 	done = 0;
 
-	if (which == ITIMER_VIRTUAL)
+	if (which == ITIMER_VIRTUAL) {
+		clock_id = CLOCK_THREAD_CPUTIME_ID;
 		signal(SIGVTALRM, sig_handler);
-	else if (which == ITIMER_PROF) {
+	} else if (which == ITIMER_PROF) {
 		clock_id = CLOCK_THREAD_CPUTIME_ID;
 		signal(SIGPROF, sig_handler);
 	}
@@ -148,7 +149,7 @@ static void check_timer_create(int which)
 	struct itimerspec val = {
 		.it_value.tv_sec = DELAY,
 	};
-	int clock_id = CLOCK_REALTIME;
+	int clock_id = which;
 	timer_t id;
 
 	done = 0;