[LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

All nanosleep POSIX conformance tests used CLOCK_REALTIME to measure
elapsed sleep duration. CLOCK_REALTIME can jump due to NTP corrections,
VM time sync, or other wall-clock adjustments, causing sporadic test
failures where measured time far exceeds expected sleep duration.

Switch to CLOCK_MONOTONIC which is immune to wall-clock changes and is
the correct clock for measuring elapsed durations.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c | 4 ++--
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c | 4 ++--
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c | 4 ++--
 .../open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c   | 4 ++--
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c | 4 ++--
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c | 4 ++--
 testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c | 4 ++--
 7 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c
index 687d01e288d914fbbdc18287746f71296c7a4327..d76451e3438e15d44ab2c2b8d0b349e666daec8c 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c
@@ -18,7 +18,7 @@ int main(void)
 	int sleepnsec = 3;
 	int slepts = 0, sleptns = 0;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
@@ -30,7 +30,7 @@ int main(void)
 		return PTS_UNRESOLVED;
 	}
 
-	if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c
index 76f31982508dc87a4f400022cd46fe766071f27d..f72cbcfbbe06a0059bbc17ad617ca76c65651a93 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c
@@ -21,7 +21,7 @@ int main(void)
 	int sleepsec = 30;
 	int pid;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
@@ -46,7 +46,7 @@ int main(void)
 			perror("Error waiting for child to exit\n");
 			return PTS_UNRESOLVED;
 		}
-		if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 			perror("Error in clock_gettime()\n");
 			return PTS_UNRESOLVED;
 		}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c
index 31ac00858018c3741758d0b5f2bf28f87aa6c1bf..07ce767123443cea2754c8b5ff2a20ed536cbfec 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c
@@ -28,7 +28,7 @@ int main(void)
 	int pid;
 	struct sigaction act;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
@@ -64,7 +64,7 @@ int main(void)
 			perror("Error waiting for child to exit\n");
 			return PTS_UNRESOLVED;
 		}
-		if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 			perror("Error in clock_gettime()\n");
 			return PTS_UNRESOLVED;
 		}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c
index 883885df434fb4ba3bb555dd565880f14623a984..8bd372f590314faa8f15fccbe5325e9fa31a6f95 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c
@@ -56,13 +56,13 @@ int main(void)
 		tssleepfor.tv_nsec = sleepvalid[i][1];
 		printf("sleep %d sec %d nsec\n",
 		       (int)tssleepfor.tv_sec, (int)tssleepfor.tv_nsec);
-		if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 			perror("Error in clock_gettime()\n");
 			return PTS_UNRESOLVED;
 		}
 
 		if (nanosleep(&tssleepfor, &tsstorage) == 0) {
-			if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+			if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 				perror("Error in clock_gettime()\n");
 				return PTS_UNRESOLVED;
 			}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c
index cce3941e7be7212ea286647ec601d3ecbb9bb85a..f44d0f938a586defa3ef244371f1850865801afa 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c
@@ -25,7 +25,7 @@ int main(void)
 	int failure = 0;
 	int slepts, sleptns;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
@@ -38,7 +38,7 @@ int main(void)
 			return PTS_UNRESOLVED;
 		}
 
-		if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 			perror("Error in clock_gettime()\n");
 			return PTS_UNRESOLVED;
 		}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c
index bfc271edf25f9cd0f343eef11b335d5da20eb646..201ab72a5d4a5a345839fb87f4f1621c70a5bb36 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c
@@ -26,7 +26,7 @@ int main(void)
 	int pid, slepts;
 	struct timespec tsbefore, tsafter;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) != 0) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) != 0) {
 		perror("clock_gettime() did not return success\n");
 		return PTS_UNRESOLVED;
 	}
@@ -74,7 +74,7 @@ int main(void)
 			return PTS_FAIL;
 		}
 
-		if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 			perror("Error in clock_gettime()\n");
 			return PTS_UNRESOLVED;
 		}
diff --git a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c
index caf4470e4a26b27ec79deed27c147e2feceffdf8..eab419591ab0c27a5d2dfb556cf2f13f7cc25e6e 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c
@@ -34,7 +34,7 @@ int main(void)
 	int pid;
 	struct sigaction act;
 
-	if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+	if (clock_gettime(CLOCK_MONOTONIC, &tsbefore) == -1) {
 		perror("Error in clock_gettime()\n");
 		return PTS_UNRESOLVED;
 	}
@@ -60,7 +60,7 @@ int main(void)
 			return CHILDFAILURE;
 		}
 
-		if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &tsafter) == -1) {
 			perror("Error in clock_gettime()\n");
 			return CHILDFAILURE;
 		}

---
base-commit: 4688c20c01eece869b59e05ca3dd68c43e0d6af7
change-id: 20260331-nanosleep_posix_fix-66162acca1ed

Best regards,
-- 
Andrea Cervesato <andrea.cervesato@suse.com>


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Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[Cyril Hrubis]

Hi!
> All nanosleep POSIX conformance tests used CLOCK_REALTIME to measure
> elapsed sleep duration. CLOCK_REALTIME can jump due to NTP corrections,
> VM time sync, or other wall-clock adjustments, causing sporadic test
> failures where measured time far exceeds expected sleep duration.
> 
> Switch to CLOCK_MONOTONIC which is immune to wall-clock changes and is
> the correct clock for measuring elapsed durations.

Unfortunately CLOCK_MONOTONIC is optional in POSIX so we have to check
if it's present at least at compile time with something as:

#if _POSIX_MONOTONIC_CLOCK
# define TEST_CLOCK CLOCK_MONOTONIC
#else
# define TEST_CLOCK CLOCK_REALTIME
#endif

-- 
Cyril Hrubis
chrubis@suse.cz

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Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[Andrea Cervesato via ltp]

Hi Cyril,

> Hi!
> > All nanosleep POSIX conformance tests used CLOCK_REALTIME to measure
> > elapsed sleep duration. CLOCK_REALTIME can jump due to NTP corrections,
> > VM time sync, or other wall-clock adjustments, causing sporadic test
> > failures where measured time far exceeds expected sleep duration.
> > 
> > Switch to CLOCK_MONOTONIC which is immune to wall-clock changes and is
> > the correct clock for measuring elapsed durations.
> 
> Unfortunately CLOCK_MONOTONIC is optional in POSIX so we have to check
> if it's present at least at compile time with something as:
> 
> #if _POSIX_MONOTONIC_CLOCK
> # define TEST_CLOCK CLOCK_MONOTONIC
> #else
> # define TEST_CLOCK CLOCK_REALTIME
> #endif

good point. If it was a non-posix project it was called non-openposix :-)

Do you think that check is enough in this case? Or we should just mark
this test (if we really want to keep it 100% posix) as XFAIL ? I really
didn't see any option but introducing CLOCK_MONOTONIC checks.

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[Cyril Hrubis]

Hi!
> > #if _POSIX_MONOTONIC_CLOCK
> > # define TEST_CLOCK CLOCK_MONOTONIC
> > #else
> > # define TEST_CLOCK CLOCK_REALTIME
> > #endif
> 
> good point. If it was a non-posix project it was called non-openposix :-)
> 
> Do you think that check is enough in this case? Or we should just mark
> this test (if we really want to keep it 100% posix) as XFAIL ? I really
> didn't see any option but introducing CLOCK_MONOTONIC checks.

Maybe we can can print a hint that we are falling back to CLOCK_REALTIME
in case that CLOCK_MONOTNIC is not there and proceed with the test.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement

[Andrea Cervesato via ltp]

> Maybe we can can print a hint that we are falling back to CLOCK_REALTIME
> in case that CLOCK_MONOTNIC is not there and proceed with the test.

Ok, I will also gate the CLOCK_MONOTONIC part in the patch for
clock_settime since it's having the same issue.

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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