[igt-dev] [PATCH i-g-t 2/3] gem_sync: Measure wakeup latency while also scheduling the next batch

[Chris Wilson]

More variants on stress waits to serve the dual purpose of investigating
different aspects of the latency (this time while also serving
execlists interrupts) while also checking that we never miss the wakeup.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 tests/gem_sync.c | 142 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/tests/gem_sync.c b/tests/gem_sync.c
index 495ca3b53..c697220ad 100644
--- a/tests/gem_sync.c
+++ b/tests/gem_sync.c
@@ -294,6 +294,144 @@ wakeup_ring(int fd, unsigned ring, int timeout, int wlen)
 	igt_assert_eq(intel_detect_and_clear_missed_interrupts(fd), 0);
 }
 
+static void
+active_wakeup_ring(int fd, unsigned ring, int timeout, int wlen)
+{
+	unsigned engines[16];
+	const char *names[16];
+	int num_engines = 0;
+
+	if (ring == ALL_ENGINES) {
+		for_each_physical_engine(fd, ring) {
+			if (!gem_can_store_dword(fd, ring))
+				continue;
+
+			names[num_engines] = e__->name;
+			engines[num_engines++] = ring;
+			if (num_engines == ARRAY_SIZE(engines))
+				break;
+		}
+		igt_require(num_engines);
+	} else {
+		gem_require_ring(fd, ring);
+		igt_require(gem_can_store_dword(fd, ring));
+		names[num_engines] = NULL;
+		engines[num_engines++] = ring;
+	}
+
+	intel_detect_and_clear_missed_interrupts(fd);
+	igt_fork(child, num_engines) {
+		const uint32_t bbe = MI_BATCH_BUFFER_END;
+		struct drm_i915_gem_exec_object2 object;
+		struct drm_i915_gem_execbuffer2 execbuf;
+		double end, this, elapsed, now, baseline;
+		unsigned long cycles;
+		igt_spin_t *spin[2];
+		uint32_t cmd;
+
+		memset(&object, 0, sizeof(object));
+		object.handle = gem_create(fd, 4096);
+		gem_write(fd, object.handle, 0, &bbe, sizeof(bbe));
+
+		memset(&execbuf, 0, sizeof(execbuf));
+		execbuf.buffers_ptr = to_user_pointer(&object);
+		execbuf.buffer_count = 1;
+		execbuf.flags = engines[child % num_engines];
+
+		spin[0] = __igt_spin_batch_new(fd,
+					       .engine = execbuf.flags,
+					       .flags = (IGT_SPIN_POLL_RUN |
+							 IGT_SPIN_FAST));
+		igt_assert(spin[0]->running);
+		cmd = *spin[0]->batch;
+
+		spin[1] = __igt_spin_batch_new(fd,
+					       .engine = execbuf.flags,
+					       .flags = (IGT_SPIN_POLL_RUN |
+							 IGT_SPIN_FAST));
+
+		gem_execbuf(fd, &execbuf);
+
+		igt_spin_batch_end(spin[1]);
+		igt_spin_batch_end(spin[0]);
+		gem_sync(fd, object.handle);
+
+		for (int warmup = 0; warmup <= 1; warmup++) {
+			*spin[0]->batch = cmd;
+			*spin[0]->running = 0;
+			gem_execbuf(fd, &spin[0]->execbuf);
+
+			end = gettime() + timeout/10.;
+			elapsed = 0;
+			cycles = 0;
+			do {
+				while (!READ_ONCE(*spin[0]->running))
+					;
+
+				*spin[1]->batch = cmd;
+				*spin[1]->running = 0;
+				gem_execbuf(fd, &spin[1]->execbuf);
+
+				this = gettime();
+				igt_spin_batch_end(spin[0]);
+				gem_sync(fd, spin[0]->handle);
+				now = gettime();
+
+				elapsed += now - this;
+				cycles++;
+				igt_swap(spin[0], spin[1]);
+			} while (now < end);
+			igt_spin_batch_end(spin[0]);
+			baseline = elapsed / cycles;
+		}
+		igt_info("%s%saseline %ld cycles: %.3f us\n",
+			 names[child % num_engines] ?: "",
+			 names[child % num_engines] ? " b" : "B",
+			 cycles, elapsed*1e6/cycles);
+
+		*spin[0]->batch = cmd;
+		*spin[0]->running = 0;
+		gem_execbuf(fd, &spin[0]->execbuf);
+
+		end = gettime() + timeout;
+		elapsed = 0;
+		cycles = 0;
+		do {
+			while (!READ_ONCE(*spin[0]->running))
+				;
+
+			for (int n = 0; n < wlen; n++)
+				gem_execbuf(fd, &execbuf);
+
+			*spin[1]->batch = cmd;
+			*spin[1]->running = 0;
+			gem_execbuf(fd, &spin[1]->execbuf);
+
+			this = gettime();
+			igt_spin_batch_end(spin[0]);
+			gem_sync(fd, object.handle);
+			now = gettime();
+
+			elapsed += now - this;
+			cycles++;
+			igt_swap(spin[0], spin[1]);
+		} while (now < end);
+		igt_spin_batch_end(spin[0]);
+		elapsed -= cycles * baseline;
+
+		igt_info("%s%sompleted %ld cycles: %.3f + %.3f us\n",
+			 names[child % num_engines] ?: "",
+			 names[child % num_engines] ? " c" : "C",
+			 cycles, 1e6*baseline, elapsed*1e6/cycles);
+
+		igt_spin_batch_free(fd, spin[1]);
+		igt_spin_batch_free(fd, spin[0]);
+		gem_close(fd, object.handle);
+	}
+	igt_waitchildren_timeout(2*timeout, NULL);
+	igt_assert_eq(intel_detect_and_clear_missed_interrupts(fd), 0);
+}
+
 static void
 store_ring(int fd, unsigned ring, int num_children, int timeout)
 {
@@ -1018,6 +1156,8 @@ igt_main
 			idle_ring(fd, e->exec_id | e->flags, 150);
 		igt_subtest_f("wakeup-%s", e->name)
 			wakeup_ring(fd, e->exec_id | e->flags, 150, 1);
+		igt_subtest_f("active-wakeup-%s", e->name)
+			active_wakeup_ring(fd, e->exec_id | e->flags, 150, 1);
 		igt_subtest_f("double-wakeup-%s", e->name)
 			wakeup_ring(fd, e->exec_id | e->flags, 150, 2);
 		igt_subtest_f("store-%s", e->name)
@@ -1050,6 +1190,8 @@ igt_main
 		store_ring(fd, ALL_ENGINES, ncpus, 150);
 	igt_subtest("wakeup-each")
 		wakeup_ring(fd, ALL_ENGINES, 150, 1);
+	igt_subtest("active-wakeup-each")
+		active_wakeup_ring(fd, ALL_ENGINES, 150, 1);
 	igt_subtest("double-wakeup-each")
 		wakeup_ring(fd, ALL_ENGINES, 150, 2);
 
-- 
2.18.0