Engine busyness samples around a 10ms period is failing with busyness ranging approx. from 87% to 115% as shown below. The expected range is +/- 5% of the sample period. Fail 10% of the time. rcs0: reported 11716042ns [91%] busyness while spinning [for 12805719ns] When determining busyness of active engine, the GuC based engine busyness implementation relies on a 64 bit timestamp register read. The latency incurred by this register read causes the failure. On DG1, when the test fails, the observed latencies range from 900us - 1.5ms. Optimizing the 2x32 read by acquiring the lock and forcewake prior to all reg reads reduces the rate of failure to around 2%, but does not eliminate it. In order to make the selftest more robust and always account for such latencies, increase the sample period to 100 ms. This eliminates the issue as seen in a 1000 runs. v2: (Ashutosh) - Add error to commit msg - Include gitlab bug - Update commit for inclusion of 2x32 optimized read Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4418 Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx> Acked-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> Reviewed-by: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx> --- drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c index 0dcb3ed44a73..87c94314cf67 100644 --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c @@ -317,7 +317,7 @@ static int live_engine_busy_stats(void *arg) ENGINE_TRACE(engine, "measuring busy time\n"); preempt_disable(); de = intel_engine_get_busy_time(engine, &t[0]); - mdelay(10); + mdelay(100); de = ktime_sub(intel_engine_get_busy_time(engine, &t[1]), de); preempt_enable(); dt = ktime_sub(t[1], t[0]); -- 2.25.1
