benchmarks/gem_syslatency: Measure unloaded latency

Also useful to know how much worse than baseline the latency is when the
gem load is applied. For slower systems, presenting in nanoseconds makes
it hard to read, so switch to microseconds for output.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 23 insertions, 15 deletions

diff --git a/benchmarks/gem_syslatency.c b/benchmarks/gem_syslatency.c
index 1a879c6f..701b4362 100644
--- a/benchmarks/gem_syslatency.c
+++ b/benchmarks/gem_syslatency.c
@@ -147,7 +147,7 @@ static void *gem_busyspin(void *arg)
 
 static double elapsed(const struct timespec *a, const struct timespec *b)
 {
-	return NSEC_PER_SEC*(b->tv_sec - a->tv_sec) + (b->tv_nsec - a ->tv_nsec);
+	return 1e9*(b->tv_sec - a->tv_sec) + (b->tv_nsec - a ->tv_nsec);
 }
 
 static void *sys_wait(void *arg)
@@ -225,10 +225,14 @@ int main(int argc, char **argv)
 	igt_stats_t cycles, mean, max;
 	int time = 10;
 	int field = -1;
+	int enable_gem_sysbusy = 1;
 	int n, c;
 
-	while ((c = getopt(argc, argv, "t:f:")) != -1) {
+	while ((c = getopt(argc, argv, "t:f:n")) != -1) {
 		switch (c) {
+		case 'n': /* dry run, measure baseline system latency */
+			enable_gem_sysbusy = 0;
+			break;
 		case 't':
 			/* How long to run the benchmark for (seconds) */
 			time = atoi(optarg);
@@ -246,13 +250,15 @@ int main(int argc, char **argv)
 	}
 
 	busy = calloc(ncpus, sizeof(*busy));
-	wait = calloc(ncpus, sizeof(*wait));
-
-	for (n = 0; n < ncpus; n++) {
-		busy[n].cpu = n;
-		pthread_create(&busy[n].thread, NULL, gem_busyspin, &busy[n]);
+	if (enable_gem_sysbusy) {
+		for (n = 0; n < ncpus; n++) {
+			busy[n].cpu = n;
+			pthread_create(&busy[n].thread, NULL,
+				       gem_busyspin, &busy[n]);
+		}
 	}
 
+	wait = calloc(ncpus, sizeof(*wait));
 	pthread_attr_init(&attr);
 	rtprio(&attr, 99);
 	for (n = 0; n < ncpus; n++) {
@@ -265,9 +271,11 @@ int main(int argc, char **argv)
 	done = 1;
 
 	igt_stats_init_with_size(&cycles, ncpus);
-	for (n = 0; n < ncpus; n++) {
-		pthread_join(busy[n].thread, NULL);
-		igt_stats_push(&cycles, busy[n].count);
+	if (enable_gem_sysbusy) {
+		for (n = 0; n < ncpus; n++) {
+			pthread_join(busy[n].thread, NULL);
+			igt_stats_push(&cycles, busy[n].count);
+		}
 	}
 
 	igt_stats_init_with_size(&mean, ncpus);
@@ -280,19 +288,19 @@ int main(int argc, char **argv)
 
 	switch (field) {
 	default:
-		printf("gem_syslatency: cycles=%.0f, latency mean=%.3fns max=%.0fns\n",
+		printf("gem_syslatency: cycles=%.0f, latency mean=%.3fus max=%.0fus\n",
 		       igt_stats_get_mean(&cycles),
-		       igt_stats_get_mean(&mean),
-		       l_estimate(&max));
+		       igt_stats_get_mean(&mean) / 1000,
+		       l_estimate(&max) / 1000);
 		break;
 	case 0:
 		printf("%.0f\n", igt_stats_get_mean(&cycles));
 		break;
 	case 1:
-		printf("%.3f\n", igt_stats_get_mean(&mean));
+		printf("%.3f\n", igt_stats_get_mean(&mean) / 1000);
 		break;
 	case 2:
-		printf("%.0f\n", l_estimate(&max));
+		printf("%.0f\n", l_estimate(&max) / 1000);
 		break;
 	}