[Intel-gfx] [PATCH i-g-t] i915/gem_exec_schedule: Try to spot unfairness

[Chris Wilson <chris@chris-wilson.co.uk>]

An important property for multi-client systems is that each client gets
a 'fair' allotment of system time. (Where fairness is at the whim of the
context properties, such as priorities.) This test forks N independent
clients (albeit they happen to share a single vm), and does an equal
amount of work in client and asserts that they take an equal amount of
time.

Though we have never claimed to have a completely fair scheduler, that
is what is expected.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
---
 tests/i915/gem_exec_schedule.c | 418 +++++++++++++++++++++++++++++++++
 1 file changed, 418 insertions(+)

diff --git a/tests/i915/gem_exec_schedule.c b/tests/i915/gem_exec_schedule.c
index 56c638833..d1121ecd2 100644
--- a/tests/i915/gem_exec_schedule.c
+++ b/tests/i915/gem_exec_schedule.c
@@ -2495,6 +2495,417 @@ 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 ns_to_ticks(int i915, uint64_t ns)
+{
+	return div64_u64_round_up(ns * read_timestamp_frequency(i915),
+				  NSEC_PER_SEC);
+}
+
+static uint64_t ticks_to_ns(int i915, uint64_t ticks)
+{
+	return div64_u64_round_up(ticks * NSEC_PER_SEC,
+				  read_timestamp_frequency(i915));
+}
+
+#define MI_INSTR(opcode, flags) (((opcode) << 23) | (flags))
+
+#define MI_MATH(x)                      MI_INSTR(0x1a, (x) - 1)
+#define MI_MATH_INSTR(opcode, op1, op2) ((opcode) << 20 | (op1) << 10 | (op2))
+/* Opcodes for MI_MATH_INSTR */
+#define   MI_MATH_NOOP                  MI_MATH_INSTR(0x000, 0x0, 0x0)
+#define   MI_MATH_LOAD(op1, op2)        MI_MATH_INSTR(0x080, op1, op2)
+#define   MI_MATH_LOADINV(op1, op2)     MI_MATH_INSTR(0x480, op1, op2)
+#define   MI_MATH_LOAD0(op1)            MI_MATH_INSTR(0x081, op1)
+#define   MI_MATH_LOAD1(op1)            MI_MATH_INSTR(0x481, op1)
+#define   MI_MATH_ADD                   MI_MATH_INSTR(0x100, 0x0, 0x0)
+#define   MI_MATH_SUB                   MI_MATH_INSTR(0x101, 0x0, 0x0)
+#define   MI_MATH_AND                   MI_MATH_INSTR(0x102, 0x0, 0x0)
+#define   MI_MATH_OR                    MI_MATH_INSTR(0x103, 0x0, 0x0)
+#define   MI_MATH_XOR                   MI_MATH_INSTR(0x104, 0x0, 0x0)
+#define   MI_MATH_STORE(op1, op2)       MI_MATH_INSTR(0x180, op1, op2)
+#define   MI_MATH_STOREINV(op1, op2)    MI_MATH_INSTR(0x580, op1, op2)
+/* Registers used as operands in MI_MATH_INSTR */
+#define   MI_MATH_REG(x)                (x)
+#define   MI_MATH_REG_SRCA              0x20
+#define   MI_MATH_REG_SRCB              0x21
+#define   MI_MATH_REG_ACCU              0x31
+#define   MI_MATH_REG_ZF                0x32
+#define   MI_MATH_REG_CF                0x33
+
+#define MI_LOAD_REGISTER_REG    MI_INSTR(0x2A, 1)
+
+static void delay(int i915,
+		  const struct intel_execution_engine2 *e,
+		  uint32_t handle,
+		  uint64_t addr,
+		  uint64_t ns)
+{
+	const int use_64b = intel_gen(intel_get_drm_devid(i915)) >= 8;
+	const uint32_t base = gem_engine_mmio_base(i915, e->name);
+#define CS_GPR(x) (base + 0x600 + 8 * (x))
+#define TIMESTAMP (base + 0x3a8)
+	enum { START_TS, NOW_TS };
+	uint32_t *map, *cs, *jmp;
+
+	igt_require(base);
+
+	cs = map = gem_mmap__device_coherent(i915, handle, 0, 4096, PROT_WRITE);
+
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(START_TS) + 4;
+	*cs++ = 0;
+	*cs++ = MI_LOAD_REGISTER_REG;
+	*cs++ = TIMESTAMP;
+	*cs++ = CS_GPR(START_TS);
+
+	if (offset_in_page(cs) & 4)
+		*cs++ = 0;
+	jmp = cs;
+
+	*cs++ = 0x5 << 23; /* MI_ARB_CHECK */
+
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(NOW_TS) + 4;
+	*cs++ = 0;
+	*cs++ = MI_LOAD_REGISTER_REG;
+	*cs++ = TIMESTAMP;
+	*cs++ = CS_GPR(NOW_TS);
+
+	*cs++ = MI_MATH(4);
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCA, MI_MATH_REG(NOW_TS));
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCB, MI_MATH_REG(START_TS));
+	*cs++ = MI_MATH_SUB;
+	*cs++ = MI_MATH_STOREINV(MI_MATH_REG(NOW_TS), MI_MATH_REG_ACCU);
+
+	*cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
+	*cs++ = CS_GPR(NOW_TS);
+	*cs++ = addr + 4000;
+	*cs++ = addr >> 32;
+
+	*cs++ = MI_COND_BATCH_BUFFER_END | MI_DO_COMPARE | (1 + use_64b);
+	*cs++ = ~ns_to_ticks(i915, ns);
+	*cs++ = addr + 4000;
+	*cs++ = addr >> 32;
+
+	*cs++ = MI_BATCH_BUFFER_START | 1 << 8 | use_64b;
+	*cs++ = addr + offset_in_page(jmp);
+	*cs++ = addr >> 32;
+
+	munmap(map, 4096);
+}
+
+static struct drm_i915_gem_exec_object2
+delay_create(int i915, uint32_t ctx,
+	     const struct intel_execution_engine2 *e,
+	     uint64_t target_ns)
+{
+	struct drm_i915_gem_exec_object2 obj = {
+		.handle = batch_create(i915),
+		.flags = EXEC_OBJECT_SUPPORTS_48B_ADDRESS,
+	};
+	struct drm_i915_gem_execbuffer2 execbuf = {
+		.buffers_ptr = to_user_pointer(&obj),
+		.buffer_count = 1,
+		.rsvd1 = ctx,
+		.flags = e->flags,
+	};
+
+	gem_execbuf(i915, &execbuf);
+	gem_sync(i915, obj.handle);
+
+	delay(i915, e, obj.handle, obj.offset, target_ns);
+
+	obj.flags |= EXEC_OBJECT_PINNED;
+	return obj;
+}
+
+static void tslog(int i915,
+		  const struct intel_execution_engine2 *e,
+		  uint32_t handle,
+		  uint64_t addr)
+{
+	const int use_64b = intel_gen(intel_get_drm_devid(i915)) >= 8;
+	const uint32_t base = gem_engine_mmio_base(i915, e->name);
+#define CS_GPR(x) (base + 0x600 + 8 * (x))
+#define CS_TIMESTAMP (base + 0x358)
+	enum { ONE, MASK, ADDR };
+	uint32_t *timestamp_lo, *addr_lo;
+	uint32_t *map, *cs;
+
+	igt_require(base);
+
+	map = gem_mmap__device_coherent(i915, handle, 0, 4096, PROT_WRITE);
+	cs = map + 512;
+
+	*cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
+	*cs++ = CS_TIMESTAMP;
+	timestamp_lo = cs;
+	*cs++ = addr;
+	*cs++ = addr >> 32;
+
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(ADDR);
+	addr_lo = cs;
+	*cs++ = addr;
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(ADDR) + 4;
+	*cs++ = addr >> 32;
+
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(ONE);
+	*cs++ = 4;
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(ONE) + 4;
+	*cs++ = 0;
+
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(MASK);
+	*cs++ = 0xfffff7ff;
+	*cs++ = MI_LOAD_REGISTER_IMM;
+	*cs++ = CS_GPR(MASK) + 4;
+	*cs++ = 0xffffffff;
+
+	*cs++ = MI_MATH(8);
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCA, MI_MATH_REG(ONE));
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCB, MI_MATH_REG(ADDR));
+	*cs++ = MI_MATH_ADD;
+	*cs++ = MI_MATH_STORE(MI_MATH_REG(ADDR), MI_MATH_REG_ACCU);
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCA, MI_MATH_REG(ADDR));
+	*cs++ = MI_MATH_LOAD(MI_MATH_REG_SRCB, MI_MATH_REG(MASK));
+	*cs++ = MI_MATH_AND;
+	*cs++ = MI_MATH_STORE(MI_MATH_REG(ADDR), MI_MATH_REG_ACCU);
+
+	*cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
+	*cs++ = CS_GPR(ADDR);
+	*cs++ = addr + offset_in_page(timestamp_lo);
+	*cs++ = addr >> 32;
+	*cs++ = 0x24 << 23 | (1 + use_64b); /* SRM */
+	*cs++ = CS_GPR(ADDR);
+	*cs++ = addr + offset_in_page(addr_lo);
+	*cs++ = addr >> 32;
+
+	*cs++ = MI_BATCH_BUFFER_END;
+
+	munmap(map, 4096);
+}
+
+static struct drm_i915_gem_exec_object2
+tslog_create(int i915, uint32_t ctx, const struct intel_execution_engine2 *e)
+{
+	struct drm_i915_gem_exec_object2 obj = {
+		.handle = batch_create(i915),
+		.flags = EXEC_OBJECT_SUPPORTS_48B_ADDRESS,
+	};
+	struct drm_i915_gem_execbuffer2 execbuf = {
+		.buffers_ptr = to_user_pointer(&obj),
+		.buffer_count = 1,
+		.rsvd1 = ctx,
+		.flags = e->flags,
+	};
+
+	gem_execbuf(i915, &execbuf);
+	gem_sync(i915, obj.handle);
+
+	tslog(i915, e, obj.handle, obj.offset);
+
+	obj.flags |= EXEC_OBJECT_PINNED;
+	return obj;
+}
+
+static int cmp_u32(const void *A, const void *B)
+{
+	const unsigned long *a = A, *b = B;
+
+	if (*a < *b)
+		return -1;
+	else if (*a > *b)
+		return 1;
+	else
+		return 0;
+}
+
+static void fair_child(int i915, uint32_t ctx,
+		       const struct intel_execution_engine2 *e,
+		       uint64_t frame_ns,
+		       int timeout,
+		       int timeline,
+		       unsigned int flags,
+		       unsigned long *ctl,
+		       unsigned long *out)
+#define F_PACING 0x1
+#define F_EXTERNAL 0x2
+{
+	const int batches_per_frame = 3;
+	struct drm_i915_gem_exec_object2 prev =
+		delay_create(i915, ctx, e, frame_ns / batches_per_frame);
+	struct drm_i915_gem_exec_object2 next =
+		delay_create(i915, ctx, e, frame_ns / batches_per_frame);
+	struct drm_i915_gem_exec_object2 ts = tslog_create(i915, ctx, e);
+	struct timespec tv = {};
+	unsigned long count = 0;
+	int p_fence = -1, n_fence = -1;
+	uint32_t *map;
+	int n;
+
+	igt_nsec_elapsed(&tv);
+	while (!READ_ONCE(*ctl)) {
+		struct drm_i915_gem_execbuffer2 execbuf = {
+			.buffers_ptr = to_user_pointer(&next),
+			.buffer_count = 1,
+			.rsvd1 = ctx,
+			.rsvd2 = -1,
+			.flags = e->flags,
+		};
+
+		if (flags & F_EXTERNAL) {
+			execbuf.rsvd2 =
+				sw_sync_timeline_create_fence(timeline, count);
+			execbuf.flags |= I915_EXEC_FENCE_IN;
+		}
+
+		execbuf.flags |= I915_EXEC_FENCE_OUT;
+		gem_execbuf_wr(i915, &execbuf);
+		n_fence = execbuf.rsvd2 >> 32;
+		execbuf.flags &= ~(I915_EXEC_FENCE_OUT | I915_EXEC_FENCE_IN);
+		for (n = 1; n < batches_per_frame; n++)
+			gem_execbuf(i915, &execbuf);
+
+		execbuf.buffers_ptr = to_user_pointer(&ts);
+		execbuf.batch_start_offset = 2048;
+		gem_execbuf(i915, &execbuf);
+
+		if (flags & F_PACING && p_fence != -1) {
+			struct pollfd pfd = {
+				.fd = p_fence,
+				.events = POLLIN,
+			};
+			poll(&pfd, 1, -1);
+		}
+		close(p_fence);
+		close(execbuf.rsvd2);
+
+		igt_swap(prev, next);
+		igt_swap(p_fence, n_fence);
+		count++;
+	}
+	gem_sync(i915, prev.handle);
+	close(p_fence);
+
+	gem_close(i915, next.handle);
+	gem_close(i915, prev.handle);
+
+	map = gem_mmap__device_coherent(i915, ts.handle, 0, 4096, PROT_WRITE);
+	for (n = 1; n < min(count, 512); n++)
+		map[n - 1] = map[n] - map[n - 1];
+	qsort(map, --n, sizeof(*map), cmp_u32);
+	*out = ticks_to_ns(i915, map[n / 2]);
+	munmap(map, 4096);
+
+	gem_close(i915, ts.handle);
+}
+
+static int cmp_ul(const void *A, const void *B)
+{
+	const unsigned long *a = A, *b = B;
+
+	if (*a < *b)
+		return -1;
+	else if (*a > *b)
+		return 1;
+	else
+		return 0;
+}
+
+static void fairness(int i915,
+		     const struct intel_execution_engine2 *e,
+		     int timeout, unsigned int flags)
+{
+	const int frame_ns = 16666 * 1000;
+	unsigned long *result;
+
+	igt_require(intel_gen(intel_get_drm_devid(i915)) >= 8);
+	igt_require(gem_class_has_mutable_submission(i915, e->class));
+
+	result = mmap(NULL, 4096, PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
+
+	for (int n = 2; n <= 16; n <<= 1) {
+		int timeline = sw_sync_timeline_create();
+		int nframes = timeout * NSEC_PER_SEC / frame_ns + 1;
+		const int nchild = n - 1; /* odd for easy medians */
+		const int lo = nchild / 4;
+		const int hi = (3 * nchild + 3) / 4 - 1;
+		struct igt_mean m;
+
+		memset(result, 0, (nchild + 1) * sizeof(result[0]));
+		igt_fork(child, nchild) {
+			uint32_t ctx = gem_context_clone_with_engines(i915, 0);
+
+			fair_child(i915, ctx, e, frame_ns / nchild,
+				   timeout, timeline, flags,
+				   &result[nchild],
+				   &result[child]);
+
+			gem_context_destroy(i915, ctx);
+		}
+
+		while (nframes--) {
+			struct timespec tv = { .tv_nsec = frame_ns };
+			nanosleep(&tv, NULL);
+			sw_sync_timeline_inc(timeline, 1);
+		}
+		result[nchild] = 1;
+		for (int child = 0; child < nchild; child++) {
+			while (!READ_ONCE(result[child])) {
+				struct timespec tv = { .tv_nsec = frame_ns };
+				nanosleep(&tv, NULL);
+				sw_sync_timeline_inc(timeline, 1);
+			}
+		}
+		igt_waitchildren();
+		close(timeline);
+
+		igt_mean_init(&m);
+		for (int child = 0; child < nchild; child++)
+			igt_mean_add(&m, result[child]);
+
+		qsort(result, nchild, sizeof(*result), cmp_ul);
+		igt_info("%d clients, range: [%.1f, %.1f], iqr: [%.1f, %.1f], median: %.1f, mean: %.1f ± %.2f ms\n",
+			 nchild,
+			 1e-6 * result[0],  1e-6 * result[nchild - 1],
+			 1e-6 * result[lo], 1e-6 * result[hi],
+			 1e-6 * result[nchild / 2],
+			 1e-6 * igt_mean_get(&m),
+			 1e-6 * sqrt(igt_mean_get_variance(&m)));
+
+#if 0
+		/* Mean within 10% of target */
+		igt_assert( 9 * igt_mean_get(&m) > 10 * frame_ns &&
+			   10 * igt_mean_get(&m) <  9 * frame_ns);
+
+		/* Variance [inter-quartile range] is less than 33% of median */
+		igt_assert(3 * result[hi] - result[lo] < result[nchild / 2]);
+#endif
+	}
+
+	munmap(result, 4096);
+}
+
 #define test_each_engine(T, i915, e) \
 	igt_subtest_with_dynamic(T) __for_each_physical_engine(i915, e) \
 		igt_dynamic_f("%s", e->name)
@@ -2589,6 +3000,13 @@ igt_main
 		test_each_engine_store("promotion", fd, e)
 			promotion(fd, e->flags);
 
+		test_each_engine_store("fair-none", fd, e)
+			fairness(fd, e, 2, 0);
+		test_each_engine_store("fair-pace", fd, e)
+			fairness(fd, e, 2, F_PACING);
+		test_each_engine_store("fair-sync", fd, e)
+			fairness(fd, e, 2, F_PACING | F_EXTERNAL);
+
 		igt_subtest_group {
 			igt_fixture {
 				igt_require(gem_scheduler_has_preemption(fd));
-- 
2.27.0.rc2

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