[PATCH v2] prime_mmap_coherency: Add return error tests for prime sync ioctl

[Chris Wilson]

On Thu, Mar 17, 2016 at 06:18:06PM -0300, Tiago Vignatti wrote:
> +static void test_ioctl_errors(void)
> +{
> +	int i;
> +	int num_children = 8*sysconf(_SC_NPROCESSORS_ONLN);
> +
> +	igt_fork_signal_helper();
> +	igt_fork(child, num_children) {

Actually there is a danger here in only using a fork-bomb, we may loose
out on signal interruptions due to busyspins on the mutex (i.e. the
contention hiding critical paths, since we crucially rely on timing).

For fun, I would use:

int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
int num_children;

igt_fork_signal_helper();
for (int num_children = 1; num_children <= 8 *ncpus; num_children <<= 1) {
	igt_fork(child, num_children) {
		struct timespec start = {};
		while (igt_seconds_elapsed(&start) <= num_children)
			blit_and_cmp();
	}
}
igt_waitchildren();
igt_stop_signal_helper();
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre