Wait for the GPU to wake up from the semaphore before measuring the time, so that we coordinate the sampling on both the CPU and GPU for more accurate comparisons. Reported-by: Bruce Chang <yu.bruce.chang@xxxxxxxxx> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: CQ Tang <cq.tang@xxxxxxxxx> --- drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 4 +++- 1 file changed, 3 insertions(+), 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 3ce8cb3329f3..007a7c790778 100644 --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c @@ -111,8 +111,10 @@ static int __measure_timestamps(struct intel_context *ce, /* Run the request for a 100us, sampling timestamps before/after */ preempt_disable(); - *dt = local_clock(); write_semaphore(&sema[2], 0); + while (READ_ONCE(sema[1]) == 0) /* wait for the gpu to catch up */ + cpu_relax(); + *dt = local_clock(); udelay(100); *dt = local_clock() - *dt; write_semaphore(&sema[2], 1); -- 2.20.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
