[igt-dev] [PATCH i-g-t] tests/perf_pmu: Use absolute tolerance in accuracy tests

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

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.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
---
 tests/perf_pmu.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
index 9ebffc64d1f1..8e547338b47c 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,
@@ -1571,7 +1579,7 @@ accuracy(int gem_fd, const struct intel_execution_engine2 *e,
 
 	/* 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));
@@ -1590,8 +1598,11 @@ 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);
+	busy_r *= 100.0;
+	expected *= 100.0;
+
+	assert_within(busy_r, expected, 2);
+	assert_within(100.0 - busy_r, 100.0 - expected, 2);
 }
 
 igt_main
-- 
2.14.1