[igt-dev] [PATCH i-g-t] i915/gem_exec_schedule: Measure timeslice distribution when oversaturated

[Chris Wilson]

Check that timeslices for an oversaturated system (where there is more
work than can be supported by a single engine) are evenly distributed
between the clients.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 tests/i915/gem_exec_schedule.c | 179 +++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)

diff --git a/tests/i915/gem_exec_schedule.c b/tests/i915/gem_exec_schedule.c
index f23d63ac3..263f1dd78 100644
--- a/tests/i915/gem_exec_schedule.c
+++ b/tests/i915/gem_exec_schedule.c
@@ -2516,6 +2516,154 @@ static void measure_semaphore_power(int i915)
 	rapl_close(&pkg);
 }
 
+static int read_timestamp_frequency(int i915)
+{
+	int value = 0;
+	drm_i915_getparam_t gp = {
+		.value = &value,
+		.param = I915_PARAM_CS_TIMESTAMP_FREQUENCY,
+	};
+	ioctl(i915, DRM_IOCTL_I915_GETPARAM, &gp);
+	return value;
+}
+
+static uint64_t div64_u64_round_up(uint64_t x, uint64_t y)
+{
+	return (x + y - 1) / y;
+}
+
+static uint64_t ticks_to_ns(int i915, uint64_t ticks)
+{
+	return div64_u64_round_up(ticks * NSEC_PER_SEC,
+				  read_timestamp_frequency(i915));
+}
+
+static int cmp_u32(const void *A, const void *B)
+{
+	const uint32_t *a = A, *b = B;
+
+	if (*a < *b)
+		return -1;
+	else if (*a > *b)
+		return 1;
+	else
+		return 0;
+}
+
+static uint32_t read_ctx_timestamp(int i915,
+				   uint32_t ctx,
+				   const struct intel_execution_engine2 *e)
+{
+	const int use_64b = intel_gen(intel_get_drm_devid(i915)) >= 8;
+	const uint32_t base = gem_engine_mmio_base(i915, e->name);
+	struct drm_i915_gem_relocation_entry reloc;
+	struct drm_i915_gem_exec_object2 obj = {
+		.handle = gem_create(i915, 4096),
+		.offset = 32 << 20,
+		.relocs_ptr = to_user_pointer(&reloc),
+		.relocation_count = 1,
+	};
+	struct drm_i915_gem_execbuffer2 execbuf = {
+		.buffers_ptr = to_user_pointer(&obj),
+		.buffer_count = 1,
+		.flags = e->flags,
+		.rsvd1 = ctx,
+	};
+#define RUNTIME (base + 0x3a8)
+	uint32_t *map, *cs;
+	uint32_t ts;
+
+	igt_require(base);
+
+	cs = map = gem_mmap__device_coherent(i915, obj.handle,
+					     0, 4096, PROT_WRITE);
+
+	*cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
+	*cs++ = RUNTIME;
+	memset(&reloc, 0, sizeof(reloc));
+	reloc.target_handle = obj.handle;
+	reloc.presumed_offset = obj.offset;
+	reloc.offset = offset_in_page(cs);
+	reloc.delta = 4000;
+	*cs++ = obj.offset + 4000;
+	*cs++ = obj.offset >> 32;
+
+	*cs++ = MI_BATCH_BUFFER_END;
+
+	gem_execbuf(i915, &execbuf);
+	gem_sync(i915, obj.handle);
+	gem_close(i915, obj.handle);
+
+	ts = map[1000];
+	munmap(map, 4096);
+
+	return ts;
+}
+
+static void fairslice(int i915,
+		      const struct intel_execution_engine2 *e,
+		      unsigned long flags,
+		      int duration)
+{
+	const double timeslice_duration_ns = 1e6;
+	igt_spin_t *spin = NULL;
+	double threshold;
+	uint32_t ctx[3];
+	uint32_t ts[3];
+
+	for (int i = 0; i < ARRAY_SIZE(ctx); i++) {
+		ctx[i] = gem_context_clone_with_engines(i915, 0);
+		if (spin == NULL) {
+			spin = __igt_spin_new(i915,
+					      .ctx = ctx[i],
+					      .engine = e->flags,
+					      .flags = flags);
+		} else {
+			struct drm_i915_gem_execbuffer2 eb = {
+				.buffer_count = 1,
+				.buffers_ptr = to_user_pointer(&spin->obj[IGT_SPIN_BATCH]),
+				.flags = e->flags,
+				.rsvd1 = ctx[i],
+			};
+			gem_execbuf(i915, &eb);
+		}
+	}
+
+	sleep(duration); /* over the course of many timeslices */
+
+	igt_assert(gem_bo_busy(i915, spin->handle));
+	igt_spin_end(spin);
+	for (int i = 0; i < ARRAY_SIZE(ctx); i++)
+		ts[i] = read_ctx_timestamp(i915, ctx[i], e);
+
+	for (int i = 0; i < ARRAY_SIZE(ctx); i++)
+		gem_context_destroy(i915, ctx[i]);
+	igt_spin_free(i915, spin);
+
+	/*
+	 * If we imagine that the timeslices are randomly distributed to
+	 * the virtual engines, we would expect the variation to be modelled
+	 * by a drunken walk; ergo sqrt(num_timeslices).
+	 */
+	threshold = sqrt(1e9 * duration / timeslice_duration_ns);
+	threshold *= timeslice_duration_ns;
+	threshold *= 2; /* CI safety factor before crying wolf */
+
+	qsort(ts, 3, sizeof(*ts), cmp_u32);
+	igt_info("%s: [%.1f, %.1f, %.1f] ms, expect %1.f +- %.1fms\n", e->name,
+		 1e-6 * ticks_to_ns(i915, ts[0]),
+		 1e-6 * ticks_to_ns(i915, ts[1]),
+		 1e-6 * ticks_to_ns(i915, ts[2]),
+		 1e3 * duration / 3,
+		 1e-6 * threshold);
+
+	igt_assert_f(ts[2], "CTX_TIMESTAMP not reported!\n");
+	igt_assert_f(ticks_to_ns(i915, ts[2] - ts[0]) < 2 * threshold,
+		     "Range of timeslices greater than tolerable: %.2fms > %.2fms; unfair!\n",
+		     1e-6 * ticks_to_ns(i915, ts[2] - ts[0]),
+		     1e-6 * threshold * 2);
+}
+
 #define test_each_engine(T, i915, e) \
 	igt_subtest_with_dynamic(T) __for_each_physical_engine(i915, e) \
 		igt_dynamic_f("%s", e->name)
@@ -2582,6 +2730,37 @@ igt_main
 		test_each_engine("lateslice", fd, e)
 			lateslice(fd, e->flags);
 
+		igt_subtest_group {
+			igt_fixture {
+				igt_require(gem_scheduler_has_semaphores(fd));
+				igt_require(gem_scheduler_has_preemption(fd));
+				igt_require(intel_gen(intel_get_drm_devid(fd)) >= 8);
+			}
+
+			test_each_engine("fairslice", fd, e)
+				fairslice(fd, e, 0, 2);
+
+			test_each_engine("u-fairslice", fd, e)
+				fairslice(fd, e, IGT_SPIN_USERPTR, 2);
+
+			igt_subtest("fairslice-all")  {
+				__for_each_physical_engine(fd, e) {
+					igt_fork(child, 1)
+						fairslice(fd, e, 0, 2);
+				}
+				igt_waitchildren();
+			}
+			igt_subtest("u-fairslice-all")  {
+				__for_each_physical_engine(fd, e) {
+					igt_fork(child, 1)
+						fairslice(fd, e,
+							  IGT_SPIN_USERPTR,
+							  2);
+				}
+				igt_waitchildren();
+			}
+		}
+
 		test_each_engine("submit-early-slice", fd, e)
 			submit_slice(fd, e, EARLY_SUBMIT);
 		test_each_engine("submit-golden-slice", fd, e)
-- 
2.29.2