On Mon, 2008-11-24 at 22:00 +0530, Sripathi Kodi wrote:
> Hi,
>
> The test case gtod_latency in realtime causes soft lockups on some
> machines. This is because the test hogs the cpus for a long time,
> because it's main loop runs at
> SCHED_FIFO, 99. We have seen soft lockups mainly on LS20 machines
> (x86_64, Opterons).
>
> The following patch introduces a sleep after some iterations of the
> test. This ensures that the test doesn't hog the cpu completely and
> hence avoids soft lockups.
>
> Testing done:
> Compiled with the patch and observed that the soft lockups are gone.
> Also observed that the latencies are not affected. In fact latencies
> improve with this patch on most hardware.
>
> Changelog:
> * Introduce periodic sleeps in the busy loop of gtod_latency to avoid soft
> lockups.
>
> Signed-off-by: Sripathi Kodi <[EMAIL PROTECTED]>
> Acked-by: John Stultz <[EMAIL PROTECTED]>
Thanks.
Regards--
Subrata
>
> diff -uprN
> ltp_cvs_24nov_org/testcases/realtime/func/gtod_latency/gtod_latency.c
> ltp_cvs_24nov/testcases/realtime/func/gtod_latency/gtod_latency.c
> --- ltp_cvs_24nov_org/testcases/realtime/func/gtod_latency/gtod_latency.c
> 2008-11-24 21:16:20.000000000 +0530
> +++ ltp_cvs_24nov/testcases/realtime/func/gtod_latency/gtod_latency.c
> 2008-11-24 21:25:33.000000000 +0530
> @@ -216,7 +216,7 @@ struct timespec stop_data[ITERATIONS];
>
> int main(int argc, char *argv[])
> {
> - int i, err;
> + int i, j, k, err;
> unsigned long long delta;
> unsigned long long max, min;
> struct sched_param param;
> @@ -262,9 +262,15 @@ int main(int argc, char *argv[])
> latency_trace_enable();
> latency_trace_start();
> }
> - for (i = 0; i < ITERATIONS; i++) {
> - clock_gettime(CLOCK_MONOTONIC,&start_data[i]);
> - clock_gettime(CLOCK_MONOTONIC,&stop_data[i]);
> + /* This loop runs for a long time, hence can cause soft lockups.
> + Calling sleep periodically avoids this. */
> + for (i=0; i<1000; i++) {
> + for (j=0; j < ITERATIONS/1000; j++) {
> + k = (i * ITERATIONS/1000) + j;
> + clock_gettime(CLOCK_MONOTONIC,&start_data[k]);
> + clock_gettime(CLOCK_MONOTONIC,&stop_data[k]);
> + }
> + usleep(1000);
> }
> for (i = 0; i < ITERATIONS; i++) {
> delta = timespec_subtract(&start_data[i], &stop_data[i]);
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