The target is that we report the vblank time accurate to within a
scanline (limit of the hw with which we can reliably compensate).
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
tests/kms_setmode.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/tests/kms_setmode.c b/tests/kms_setmode.c
index 9dafca0..e1e1893 100644
--- a/tests/kms_setmode.c
+++ b/tests/kms_setmode.c
@@ -417,6 +417,11 @@ static double frame_time(const drmModeModeInfo *kmode)
return 1000.0 * kmode->htotal * kmode->vtotal / kmode->clock;
}
+static double line_time(const drmModeModeInfo *kmode)
+{
+ return 1000.0 * kmode->htotal / kmode->clock;
+}
+
static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
{
#define CALIBRATE_TS_STEPS 120 /* ~2s has to be less than 128! */
@@ -425,6 +430,7 @@ static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
uint32_t last_seq;
uint64_t last_timestamp;
double expected;
+ double accuracy;
double mean;
double stddev;
int n;
@@ -470,15 +476,21 @@ static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
mean = igt_stats_get_mean(&stats);
stddev = igt_stats_get_std_deviation(&stats);
+ accuracy = 3.090 * stddev; /* 2-tailed 99% confidence */
+
+ igt_info("Expected frametime: %.0fus; measured %.1fus +- %.3fus accuracy %.2f%% [%.2f scanlines]\n",
+ expected, mean, stddev,
+ 100 * accuracy / mean, accuracy / line_time(kmode));
- igt_info("Expected frametime: %.0fus; measured %.1fus +- %.3fus accuracy %.2f%%\n",
- expected, mean, stddev, 100 * 6 * stddev / mean);
- igt_assert(6 * stddev / mean < 0.005); /* 99% accuracy within 0.5% */
+ /* 99% accuracy within one scanline */
+ igt_assert_f(accuracy < line_time(kmode),
+ "vblank accuracy (%.3fus, %.1f%%) worse than a scanline (%.3fus)\n",
+ accuracy, 100 * accuracy / mean, line_time(kmode));
igt_assert_f(fabs(mean - expected) < 2*stddev,
- "vblank interval differs from modeline! expected %.1fus, measured %1.fus +- %.3fus, difference %.1fus (%.1f sigma)\n",
- expected, mean, stddev,
- fabs(mean - expected), fabs(mean - expected) / stddev);
+ "vblank interval differs from modeline! expected %.1fus, measured %1.fus +- %.3fus, difference %.1fus (%.1f sigma)\n",
+ expected, mean, stddev,
+ fabs(mean - expected), fabs(mean - expected) / stddev);
}
static void test_crtc_config(const struct test_config *tconf,
--
2.10.2
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