[igt-dev] [PATCH i-g-t] tests/gem_exec_latency: New subtests for checking submission from RT tasks

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

We want to make sure RT tasks which use a lot of CPU times can submit
batch buffers with roughly the same latency (and certainly not worse)
compared to normal tasks.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
---
 tests/gem_exec_latency.c | 176 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 176 insertions(+)

diff --git a/tests/gem_exec_latency.c b/tests/gem_exec_latency.c
index 9498c0921e60..420ede0f83a0 100644
--- a/tests/gem_exec_latency.c
+++ b/tests/gem_exec_latency.c
@@ -36,11 +36,15 @@
 #include <sys/time.h>
 #include <sys/signal.h>
 #include <time.h>
+#include <sched.h>
 
 #include "drm.h"
 
 #include "igt_sysfs.h"
 #include "igt_vgem.h"
+#include "igt_dummyload.h"
+#include "igt_stats.h"
+
 #include "i915/gem_ring.h"
 
 #define LOCAL_I915_EXEC_NO_RELOC (1<<11)
@@ -351,6 +355,172 @@ static void latency_from_ring(int fd,
 	}
 }
 
+static void __rearm_spin_batch(igt_spin_t *spin)
+{
+	const uint32_t mi_arb_chk = 0x5 << 23;
+
+       *spin->batch = mi_arb_chk;
+       *spin->running = 0;
+       __sync_synchronize();
+}
+
+static void
+__submit_spin_batch(int fd, igt_spin_t *spin, unsigned int flags)
+{
+	struct drm_i915_gem_execbuffer2 eb = spin->execbuf;
+
+	eb.flags &= ~(0x3f | I915_EXEC_BSD_MASK);
+	eb.flags |= flags | I915_EXEC_NO_RELOC;
+
+	gem_execbuf(fd, &eb);
+}
+
+struct rt_pkt
+{
+#define RT_OK (0)
+#define RT_FAIL (1)
+#define RT_TIMEOUT (2)
+	int status;
+	struct igt_mean mean;
+	double max;
+};
+
+static void __spin_wait(struct rt_pkt *msg, igt_spin_t *spin, double *t_wait)
+{
+	struct timespec ts = { };
+	uint64_t t_last = 0;
+
+	igt_nsec_elapsed(&ts);
+
+	while (!READ_ONCE(*spin->running)) {
+		uint64_t t = igt_nsec_elapsed(&ts);
+
+		if ((t - t_last) > 5UL * NSEC_PER_SEC) {
+			 /* Absolute timeout to save time. */
+			msg->status = RT_TIMEOUT;
+		} else if ((t - t_last) > NSEC_PER_SEC / 10) {
+			/* Backoff every 100ms to give it chance to complete. */
+			t_last = t;
+			usleep(1);
+		}
+	}
+
+	*t_wait = igt_nsec_elapsed(&ts) / 1e9;
+
+	msg->status = RT_OK;
+}
+
+/*
+ * Test whether RT thread which hogs the CPU a lot can submit work with
+ * reasonable latency.
+ */
+static void
+rthog_latency_on_ring(int fd, unsigned int ring, const char *name)
+{
+	const char *passname[] = { "warmup", "normal", "rt" };
+	struct rt_pkt res[3];
+	unsigned int i;
+	int link[2];
+	int ret;
+
+	igt_require(gem_can_store_dword(fd, ring));
+
+	igt_assert(pipe(link) == 0);
+
+	memset(res, 0, sizeof(res));
+
+        igt_fork(child, 1) {
+		unsigned int pass = 0; /* Three passes: warmup, normal, rt. */
+
+		do {
+			struct rt_pkt msg = { };
+			igt_spin_t *spin;
+
+			igt_mean_init(&msg.mean);
+
+			if (pass == 2) {
+				struct sched_param rt =
+						{ .sched_priority = 99 };
+
+				ret = sched_setscheduler(0,
+							SCHED_FIFO | SCHED_RESET_ON_FORK,
+							&rt);
+				if (ret) {
+					igt_warn("Failed to set scheduling policy!\n");
+					msg.status = RT_FAIL;
+					write(link[1], &msg, sizeof(msg));
+					exit(1);
+				}
+			}
+
+			spin = __igt_spin_batch_new_poll(fd, 0, ring);
+			if (!spin) {
+				igt_warn("Failed to create spinner! (%s)\n",
+					 passname[pass]);
+				msg.status = RT_FAIL;
+				write(link[1], &msg, sizeof(msg));
+				exit(1);
+			}
+			igt_spin_busywait_until_running(spin);
+
+			igt_until_timeout(pass > 0 ? 5 : 2) {
+				double t;
+
+				igt_spin_batch_end(spin);
+				gem_sync(fd, spin->handle);
+
+				__rearm_spin_batch(spin);
+				__submit_spin_batch(fd, spin, ring);
+
+				__spin_wait(&msg, spin, &t);
+				if (msg.status != RT_OK) {
+					igt_warn("Wait timeout! (%s)\n",
+						 passname[pass]);
+					write(link[1], &msg, sizeof(msg));
+					exit(1);
+				}
+
+				if (t > msg.max)
+					msg.max = t;
+
+				igt_mean_add(&msg.mean, t);
+			}
+
+			igt_spin_batch_free(fd, spin);
+
+			igt_info("%10s: mean=%.2fus variance=%.2fus max=%.2fus (n=%lu)\n",
+				 passname[pass],
+				 igt_mean_get(&msg.mean) * 1e6,
+				 igt_mean_get_variance(&msg.mean) * 1e6,
+				 msg.max * 1e6,
+				 msg.mean.count);
+
+			write(link[1], &msg, sizeof(msg));
+		} while (++pass < 3);
+
+		exit(0);
+	}
+
+	for (i = 0; i < 3; i++) {
+		ret = read(link[0], &res[i], sizeof(res[0]));
+		igt_assert_eq(ret, sizeof(res[0]));
+
+		igt_assert_eq(res[i].status, RT_OK);
+	}
+
+	close(link[0]);
+	close(link[1]);
+
+	igt_waitchildren();
+
+	/*
+	 * Check that the submission latency variance for a task with RT
+	 * priority is no larger than three times the same of a normal task.
+	 */
+	igt_assert(igt_mean_get_variance(&res[2].mean) <
+		   igt_mean_get_variance(&res[1].mean) * 3);
+}
+
 igt_main
 {
 	const struct intel_execution_engine *e;
@@ -391,6 +561,12 @@ igt_main
 							e->exec_id | e->flags,
 							e->name, 0);
 
+				igt_subtest_f("%s-rthog-submit", e->name)
+					rthog_latency_on_ring(device,
+							      e->exec_id |
+							      e->flags,
+							      e->name);
+
 				igt_subtest_f("%s-dispatch-queued", e->name)
 					latency_on_ring(device,
 							e->exec_id | e->flags,
-- 
2.14.1