tests/perf_pmu: Use absolute tolerance in accuracy tests

We need to use absolute tolerance when asserting on percentages. Relative
tolerance in this case is unfair and inaccurate since it's strictness
varies with relative target busyness.

v2:
 * Do not include spin batch edit and submit into measured time.
 * Open PMU before child is in test PWM phase.
 * No need to emit test PWM for twice as long with the new explicit
   synchroniazation via pipe.
 * Log test duration in ms for better readability.
 * Drop inverse assert. (Chris Wilson)

v3: Explain tasklet delay. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 26 insertions, 14 deletions

diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
index 9ebffc64..19fcc95f 100644
--- a/tests/perf_pmu.c
+++ b/tests/perf_pmu.c
@@ -1459,7 +1459,15 @@ static void __rearm_spin_batch(igt_spin_t *spin)
        __sync_synchronize();
 }
 
-#define div_round_up(a, b) (((a) + (b) - 1) / (b))
+#define __assert_within(x, ref, tol_up, tol_down) \
+	igt_assert_f((double)(x) <= ((double)(ref) + (tol_up)) && \
+		     (double)(x) >= ((double)(ref) - (tol_down)), \
+		     "%f not within +%f/-%f of %f! ('%s' vs '%s')\n", \
+		     (double)(x), (double)(tol_up), (double)(tol_down), \
+		     (double)(ref), #x, #ref)
+
+#define assert_within(x, ref, tolerance) \
+	__assert_within(x, ref, tolerance, tolerance)
 
 static void
 accuracy(int gem_fd, const struct intel_execution_engine2 *e,
@@ -1493,8 +1501,8 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 	while (test_us < min_test_us)
 		test_us += busy_us + idle_us;
 
-	igt_info("calibration=%luus, test=%luus; ratio=%.2f%% (%luus/%luus)\n",
-		 pwm_calibration_us, test_us,
+	igt_info("calibration=%lums, test=%lums; ratio=%.2f%% (%luus/%luus)\n",
+		 pwm_calibration_us / 1000, test_us / 1000,
 		 (double)busy_us / (busy_us + idle_us) * 100.0,
 		 busy_us, idle_us);
 
@@ -1507,7 +1515,7 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 	igt_fork(child, 1) {
 		struct sched_param rt = { .sched_priority = 99 };
 		const unsigned long timeout[] = {
-			pwm_calibration_us * 1000, test_us * 2 * 1000
+			pwm_calibration_us * 1000, test_us * 1000
 		};
 		struct drm_i915_gem_exec_object2 obj = {};
 		uint64_t total_busy_ns = 0, total_idle_ns = 0;
@@ -1537,19 +1545,23 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 
 			igt_nsec_elapsed(&test_start);
 			do {
-				struct timespec t_busy = { };
-				unsigned int target_idle_us;
-
-				igt_nsec_elapsed(&t_busy);
+				unsigned int target_idle_us, t_busy;
 
 				/* Restart the spinbatch. */
 				__rearm_spin_batch(spin);
 				__submit_spin_batch(gem_fd, &obj, e);
-				measured_usleep(busy_us);
+
+				/*
+				 * Note that the submission may be delayed to a
+				 * tasklet (ksoftirqd) which cannot run until we
+				 * sleep as we hog the cpu (we are RT).
+				 */
+
+				t_busy = measured_usleep(busy_us);
 				igt_spin_batch_end(spin);
 				gem_sync(gem_fd, obj.handle);
 
-				total_busy_ns += igt_nsec_elapsed(&t_busy);
+				total_busy_ns += t_busy;
 
 				target_idle_us =
 					(100 * total_busy_ns / target_busy_pct - (total_busy_ns + total_idle_ns)) / 1000;
@@ -1569,12 +1581,13 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 		igt_spin_batch_free(gem_fd, spin);
 	}
 
+	fd = open_pmu(I915_PMU_ENGINE_BUSY(e->class, e->instance));
+
 	/* Let the child run. */
 	read(link[0], &expected, sizeof(expected));
-	assert_within_epsilon(expected, target_busy_pct/100., 0.05);
+	assert_within(100.0 * expected, target_busy_pct, 5);
 
 	/* Collect engine busyness for an interesting part of child runtime. */
-	fd = open_pmu(I915_PMU_ENGINE_BUSY(e->class, e->instance));
 	val[0] = __pmu_read_single(fd, &ts[0]);
 	read(link[0], &expected, sizeof(expected));
 	val[1] = __pmu_read_single(fd, &ts[1]);
@@ -1590,8 +1603,7 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 	igt_info("error=%.2f%% (%.2f%% vs %.2f%%)\n",
 		 __error(busy_r, expected), 100 * busy_r, 100 * expected);
 
-	assert_within_epsilon(busy_r, expected, 0.15);
-	assert_within_epsilon(1 - busy_r, 1 - expected, 0.15);
+	assert_within(100.0 * busy_r, 100.0 * expected, 2);
 }
 
 igt_main