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From: Chris Wilson <chris@chris-wilson.co.uk>
To: intel-gfx@lists.freedesktop.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Subject: [Intel-gfx] [PATCH] drm/i915/selftest: Synchronise with the GPU timestamp
Date: Fri,  5 Feb 2021 00:04:37 +0000	[thread overview]
Message-ID: <20210205000437.16079-1-chris@chris-wilson.co.uk> (raw)

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@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: CQ Tang <cq.tang@intel.com>
---
 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

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             reply	other threads:[~2021-02-05  0:04 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-05  0:04 Chris Wilson [this message]
2021-02-05  0:35 ` [Intel-gfx] [PATCH] drm/i915/selftest: Synchronise with the GPU timestamp Chang, Yu bruce
2021-02-05  3:26 ` [Intel-gfx] ✗ Fi.CI.BAT: failure for " Patchwork

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