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drm/i915/selftest: Synchronise with the GPU timestamp

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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 <yu.bruce.chang@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: CQ Tang <cq.tang@intel.com>
Reviewed-by: Bruce Chang <yu.bruce.chang@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205112912.22978-1-chris@chris-wilson.co.uk
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Chris Wilson 2021-02-05 11:29:12 +00:00 committed by Daniel Vetter
parent dc43040012
commit 985458d706
1 changed files with 5 additions and 3 deletions
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8
drivers/gpu/drm/i915/gt/selftest_engine_pm.c
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@ -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);