From 985458d706bd86c16234bfc155535da2a64a9dde Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 5 Feb 2021 11:29:12 +0000 Subject: [PATCH] drm/i915/selftest: Synchronise with the GPU timestamp 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. v2: Switch to local_irq_disable() as once suggested by Mika. Reported-by: Bruce Chang Signed-off-by: Chris Wilson Cc: CQ Tang Reviewed-by: Bruce Chang Link: https://patchwork.freedesktop.org/patch/msgid/20210205112912.22978-1-chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c index 41dc1a542cd69..2c898622bdfb4 100644 --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c @@ -110,13 +110,15 @@ static int __measure_timestamps(struct intel_context *ce, cpu_relax(); /* Run the request for a 100us, sampling timestamps before/after */ - preempt_disable(); - *dt = local_clock(); + local_irq_disable(); 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); - preempt_enable(); + local_irq_enable(); if (i915_request_wait(rq, 0, HZ / 2) < 0) { i915_request_put(rq); -- 2.30.2