[igt-dev] [PATCH i-g-t 2/2] igt/gem_sync: Alternate stress for nop+sync

[Chris Wilson]

Apply a different sort of stress by timing how long it takes to sync a
second nop batch in the pipeline. We first start a spinner on the
engine, then when we know the GPU is active, we submit the second nop;
start timing as we then release the spinner and wait for the nop to
complete.

As with every other gem_sync test, it serves two roles. The first is
that it checks that we do not miss a wakeup under common stressful
conditions (the more conditions we check, the happier we will be that
they do not occur in practice). And the second role it fulfils, is that
it provides a very crude estimate for how long it takes for a nop to
execute from a running start (we already have a complimentary estimate
for an idle start).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 tests/gem_sync.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/tests/gem_sync.c b/tests/gem_sync.c
index 1e2e089a1..4cd97c58b 100644
--- a/tests/gem_sync.c
+++ b/tests/gem_sync.c
@@ -177,6 +177,92 @@ idle_ring(int fd, unsigned ring, int timeout)
 	gem_close(fd, object.handle);
 }
 
+static void
+wakeup_ring(int fd, unsigned ring, int timeout)
+{
+	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;
+		unsigned long cycles;
+		uint32_t cmd;
+		igt_spin_t *spin;
+
+		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 = __igt_spin_batch_new_poll(fd, 0, execbuf.flags);
+		igt_assert(spin->running);
+		cmd = *spin->batch;
+
+		gem_execbuf(fd, &execbuf);
+
+		igt_spin_batch_end(spin);
+		gem_sync(fd, object.handle);
+
+		end = gettime() + timeout;
+		elapsed = 0;
+		cycles = 0;
+		do {
+			*spin->batch = cmd;
+			*spin->running = 0;
+			gem_execbuf(fd, &spin->execbuf);
+			while (!READ_ONCE(*spin->running))
+				;
+
+			gem_execbuf(fd, &execbuf);
+
+			this = gettime();
+			igt_spin_batch_end(spin);
+			gem_sync(fd, object.handle);
+			now = gettime();
+
+			elapsed += now - this;
+			cycles++;
+		} while (now < end);
+
+		igt_info("%s%sompleted %ld cycles: %.3f us\n",
+			 names[child % num_engines] ?: "",
+			 names[child % num_engines] ? " c" : "C",
+			 cycles, elapsed*1e6/cycles);
+
+		igt_spin_batch_free(fd, spin);
+		gem_close(fd, object.handle);
+	}
+	igt_waitchildren_timeout(timeout+10, 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)
 {
@@ -762,6 +848,8 @@ igt_main
 			sync_ring(fd, e->exec_id | e->flags, 1, 150);
 		igt_subtest_f("idle-%s", e->name)
 			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);
 		igt_subtest_f("store-%s", e->name)
 			store_ring(fd, e->exec_id | e->flags, 1, 150);
 		igt_subtest_f("many-%s", e->name)
@@ -782,6 +870,8 @@ igt_main
 		sync_ring(fd, ALL_ENGINES, ncpus, 150);
 	igt_subtest("forked-store-each")
 		store_ring(fd, ALL_ENGINES, ncpus, 150);
+	igt_subtest("wakeup-each")
+		wakeup_ring(fd, ALL_ENGINES, 150);
 
 	igt_subtest("basic-all")
 		sync_all(fd, 1, 5);
-- 
2.18.0.rc2