Mark Hounschell wrote:
> Before asking this on the lkml and waisting peoples time I thought I
> would seek advice here first. I am experimenting with Ingo Molnars rt
> patch which among other things, includes high res timer support. I'm not
> having a problems with the timers them selves but am seeing an anomaly
> with clock_nanosleep. It seems to return early. I have a short sample
> program that shows the anomaly. Could someone tell me if I am crazy,
> just plain wrong, or maybe even right? I am running the 2.6.16-rt23
> patch and have the userland high-res timers hooks in place. The
> following program shows early returns on every 2.6.16-rt23 box I have
> tried it on. I don't want to bother the developers if my program is
> broken so if anyone can advise I would appreciate it.
>
> Thanks and regards
> Mark
>
> To build this:
>
> cc hr_nsleep.c -o hr_nsleep -lposix-time
>
>
> #include <stdlib.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <posix_time.h>
>
> int64_t get_nsec_64();
>
> #define MAX_FAILURES 50
>
> int main()
> {
> int64_t start_nsecs;
> int64_t elapsed_nsecs;
> int64_t latency_nsecs;
> int32_t i, x;
> int32_t failures = 0;
> struct timespec tim;
>
> int64_t failed_elapsed_nsecs[MAX_FAILURES];
> int64_t failed_latency_nsecs[MAX_FAILURES];
> struct timespec failed_sleeps[MAX_FAILURES];
>
> struct timespec sleep[16] = {
> {0, 10 * 1000},
> {0, 20 * 1000},
> {0, 40 * 1000},
> {0, 80 * 1000},
> {0, 100 * 1000},
> {0, 200 * 1000},
> {0, 400 * 1000},
> {0, 800 * 1000},
> {0, 1000 * 1000},
> {0, 2000 * 1000},
> {0, 4000 * 1000},
> {0, 8000 * 1000},
> {0, 10000 * 1000},
> {0, 20000 * 1000},
> {0, 40000 * 1000},
> {0, 80000 * 1000},
> };
>
> for (x = 0; x < 10000; x++) {
> for (i = 0; i < 16; i++) {
Its because of the time it takes to get from here
> clock_gettime(CLOCK_MONOTONIC, &tim);
> tim.tv_sec += sleep[i].tv_sec;
> tim.tv_nsec += sleep[i].tv_nsec;
> if (tim.tv_nsec > 1000000000) {
> tim.tv_sec++;
> tim.tv_nsec -= 1000000000;
> }
> start_nsecs = get_nsec_64();
to here in conjunction with the use of the TIMER_ABSTIME flag.
> while (clock_nanosleep(CLOCK_MONOTONIC,
> TIMER_ABSTIME,
> &tim, NULL) && errno == EINTR);
> elapsed_nsecs = (get_nsec_64() - start_nsecs);
> latency_nsecs =
> (elapsed_nsecs -
> (int64_t)(sleep[i].tv_nsec));
> if (latency_nsecs <= 0) {
> failed_elapsed_nsecs[failures] = elapsed_nsecs;
> failed_latency_nsecs[failures] = latency_nsecs;
> failed_sleeps[failures] = sleep[i];
> failures++;
> }
> if (failures >= MAX_FAILURES) break;
> }
> if (failures >= MAX_FAILURES) break;
> }
> for (i = 0; i < failures; i++) {
> printf("\nAttempted sleep of %8d nsecs.\n" \
> "Actual sleep %8lld nsecs. BAD %8lld nsecs\n",
> (int32_t) failed_sleeps[i].tv_nsec,
> failed_elapsed_nsecs[i], failed_latency_nsecs[i]);
> }
> exit(0);
> }
>
> int64_t get_nsec_64()
> {
> int64_t ret;
> struct timespec ts;
>
> clock_gettime(CLOCK_MONOTONIC, &ts);
> ret = (int64_t) (((int64_t) ts.tv_sec * 1000000000) +
> (int64_t) ts.tv_nsec);
> return (ret);
> }
>
>
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