On Wed, Jul 08 2026 at 12:15, Wake Liu wrote:
> The posix_timers test compares the elapsed real time (GTOD) with the
> expected timer delay to verify if the timer expired. This works fine for
> real-time timers (ITIMER_REAL), but is flaky for CPU-time timers
> (ITIMER_PROF, ITIMER_VIRTUAL, and CLOCK_*_CPUTIME_ID) on loaded systems
> (like shared test runners) because the test process might be scheduled
> out, resulting in elapsed real time being larger than the consumed CPU
> time.
>
> Fix this by using the appropriate measurement method for each timer:
> - Use CPU process/thread time (via clock_gettime or getrusage) for CPU
> timers.
> - Keep using monotonic clock (real time) for real-time timers.
>
> This makes the test robust against scheduling delays.
Lacks Signed-off-by ....
> +#include <sys/resource.h>
> +
> +static long long get_clock_time_us(clockid_t clock_id)
> +{
> + struct timespec ts;
Newline between declaration and code.
> + if (clock_gettime(clock_id, &ts) < 0)
> + return -1;
> + return (long long)ts.tv_sec * USECS_PER_SEC + ts.tv_nsec / 1000;
> +}
> +
> +static long long get_itimer_time_us(int which)
> +{
> + struct rusage usage;
> +
> + switch (which) {
> + case ITIMER_REAL:
> + return get_clock_time_us(CLOCK_MONOTONIC);
> + case ITIMER_PROF:
> + return get_clock_time_us(CLOCK_PROCESS_CPUTIME_ID);
> + case ITIMER_VIRTUAL:
> + if (getrusage(RUSAGE_SELF, &usage) < 0)
> + return -1;
> + return (long long)usage.ru_utime.tv_sec * USECS_PER_SEC +
> usage.ru_utime.tv_usec;
> + default:
> + return -1;
> + }
> +}
> +
> +static int check_diff_us(long long start, long long end)
> {
> long long diff;
>
> - diff = end.tv_usec - start.tv_usec;
> - diff += (end.tv_sec - start.tv_sec) * USECS_PER_SEC;
> + diff = end - start;
Move that to the declaration line.
> if (llabs(diff - DELAY * USECS_PER_SEC) > USECS_PER_SEC / 2) {
> printf("Diff too high: %lld..", diff);
> @@ -100,7 +123,7 @@ static int check_diff(struct timeval start, struct
> timeval end)
>
> - if (gettimeofday(&end, NULL) < 0)
> - fatal_error(name, "gettimeofday()");
> + end = get_clock_time_us(which);
> + if (end < 0)
> + fatal_error(name, "get_clock_time_us()");
>
> - ksft_test_result(check_diff(start, end) == 0,
> + ksft_test_result(check_diff_us(start, end) == 0,
> "timer_create() per %s\n", name);
Please get rid of the line break.
