* [LTP] [PATCH v2] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement
@ 2026-03-31 12:42 Andrea Cervesato
2026-03-31 13:48 ` Cyril Hrubis
0 siblings, 1 reply; 3+ messages in thread
From: Andrea Cervesato @ 2026-03-31 12:42 UTC (permalink / raw)
To: Linux Test Project; +Cc: Claude
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. Guard with
_POSIX_MONOTONIC_CLOCK and fall back to CLOCK_REALTIME with a warning
on systems where CLOCK_MONOTONIC is unavailable.
Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
Changes in v2:
- introduce TEST_CLOCK to select the right available clock type
- print a message in case CLOCK_MONOTONIC is not available
- Link to v1: https://lore.kernel.org/r/20260331-nanosleep_posix_fix-v1-1-7a707f871582@suse.com
---
.../conformance/interfaces/nanosleep/1-1.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/1-2.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/1-3.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/10000-1.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/2-1.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/3-2.c | 14 ++++++++++++--
.../conformance/interfaces/nanosleep/7-2.c | 14 ++++++++++++--
7 files changed, 84 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..75b34346f13d9b62e2333dbc78023a812fc9c908 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-1.c
@@ -12,13 +12,23 @@
#include <time.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
int main(void)
{
struct timespec tssleepfor, tsstorage, tsbefore, tsafter;
int sleepnsec = 3;
int slepts = 0, sleptns = 0;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) == -1) {
perror("Error in clock_gettime()\n");
return PTS_UNRESOLVED;
}
@@ -30,7 +40,7 @@ int main(void)
return PTS_UNRESOLVED;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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..4a38bd507bba47792b942feb53954b95e92dc222 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-2.c
@@ -15,13 +15,23 @@
#include <sys/wait.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
int main(void)
{
struct timespec tssleepfor, tsstorage, tsbefore, tsafter;
int sleepsec = 30;
int pid;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) == -1) {
perror("Error in clock_gettime()\n");
return PTS_UNRESOLVED;
}
@@ -46,7 +56,7 @@ int main(void)
perror("Error waiting for child to exit\n");
return PTS_UNRESOLVED;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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..7d5600788d6bc4682f228ccc7c669576827c397a 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/1-3.c
@@ -16,6 +16,12 @@
#include <sys/wait.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
static void handler(int signo PTS_ATTRIBUTE_UNUSED)
{
printf("In handler\n");
@@ -28,7 +34,11 @@ int main(void)
int pid;
struct sigaction act;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) == -1) {
perror("Error in clock_gettime()\n");
return PTS_UNRESOLVED;
}
@@ -64,7 +74,7 @@ int main(void)
perror("Error waiting for child to exit\n");
return PTS_UNRESOLVED;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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..ebcf366acb52fd149f19951a6e4e0764bd503807 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/10000-1.c
@@ -19,6 +19,12 @@
#include <errno.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
#define NUMVALID 6
#define NUMINVALID 7
@@ -51,18 +57,22 @@ int main(void)
int failure = 0;
int slepts = 0, sleptns = 0;
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
for (i = 0; i < NUMVALID; i++) {
tssleepfor.tv_sec = sleepvalid[i][0];
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(TEST_CLOCK, &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(TEST_CLOCK, &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..8586e0ecec023029b60bce8ad5e1e72206daee34 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/2-1.c
@@ -13,6 +13,12 @@
#include <time.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
#define NUMINTERVALS 13
int main(void)
{
@@ -25,7 +31,11 @@ int main(void)
int failure = 0;
int slepts, sleptns;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) == -1) {
perror("Error in clock_gettime()\n");
return PTS_UNRESOLVED;
}
@@ -38,7 +48,7 @@ int main(void)
return PTS_UNRESOLVED;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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..1329a7e988055ed3815e4e4037f331f576264d1a 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/3-2.c
@@ -16,6 +16,12 @@
#include <stdlib.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
#define SLEEPSEC 5
#define CHILDPASS 0 //if interrupted, child will return 0
@@ -26,7 +32,11 @@ int main(void)
int pid, slepts;
struct timespec tsbefore, tsafter;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) != 0) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) != 0) {
perror("clock_gettime() did not return success\n");
return PTS_UNRESOLVED;
}
@@ -74,7 +84,7 @@ int main(void)
return PTS_FAIL;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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..70eeca9ff8eb10ac052b81f102853747a5066685 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/nanosleep/7-2.c
@@ -17,6 +17,12 @@
#include <stdlib.h>
#include "posixtest.h"
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define TEST_CLOCK CLOCK_MONOTONIC
+#else
+#define TEST_CLOCK CLOCK_REALTIME
+#endif
+
#define CHILDSUCCESS 1
#define CHILDFAILURE 0
@@ -34,7 +40,11 @@ int main(void)
int pid;
struct sigaction act;
- if (clock_gettime(CLOCK_REALTIME, &tsbefore) == -1) {
+#ifndef _POSIX_MONOTONIC_CLOCK
+ printf("CLOCK_MONOTONIC unavailable, test may fail due to external clock adjustments\n");
+#endif
+
+ if (clock_gettime(TEST_CLOCK, &tsbefore) == -1) {
perror("Error in clock_gettime()\n");
return PTS_UNRESOLVED;
}
@@ -60,7 +70,7 @@ int main(void)
return CHILDFAILURE;
}
- if (clock_gettime(CLOCK_REALTIME, &tsafter) == -1) {
+ if (clock_gettime(TEST_CLOCK, &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>
--
Mailing list info: https://lists.linux.it/listinfo/ltp
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [LTP] [PATCH v2] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement
2026-03-31 12:42 [LTP] [PATCH v2] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement Andrea Cervesato
@ 2026-03-31 13:48 ` Cyril Hrubis
2026-03-31 14:40 ` Andrea Cervesato via ltp
0 siblings, 1 reply; 3+ messages in thread
From: Cyril Hrubis @ 2026-03-31 13:48 UTC (permalink / raw)
To: Andrea Cervesato; +Cc: Claude, Linux Test Project
Hi!
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
--
Cyril Hrubis
chrubis@suse.cz
--
Mailing list info: https://lists.linux.it/listinfo/ltp
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [LTP] [PATCH v2] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement
2026-03-31 13:48 ` Cyril Hrubis
@ 2026-03-31 14:40 ` Andrea Cervesato via ltp
0 siblings, 0 replies; 3+ messages in thread
From: Andrea Cervesato via ltp @ 2026-03-31 14:40 UTC (permalink / raw)
To: Cyril Hrubis; +Cc: Claude, Linux Test Project
Merged, thanks.
--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com
--
Mailing list info: https://lists.linux.it/listinfo/ltp
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-03-31 12:42 [LTP] [PATCH v2] nanosleep: Use CLOCK_MONOTONIC for elapsed time measurement Andrea Cervesato
2026-03-31 13:48 ` Cyril Hrubis
2026-03-31 14:40 ` Andrea Cervesato via ltp
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