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* [PATCH] drm/i915: Use ktime on wait_for
@ 2018-04-20  9:54 Mika Kuoppala
  2018-04-20 10:23 ` Sagar Arun Kamble
                   ` (3 more replies)
  0 siblings, 4 replies; 10+ messages in thread
From: Mika Kuoppala @ 2018-04-20  9:54 UTC (permalink / raw)
  To: intel-gfx

We use jiffies to determine when wait expires. However
Imre did find out that jiffies can and will do a >1
increments on certain situations [1]. When this happens
in a wait_for loop, we return timeout errorneously
much earlier than what the real wallclock would say.

We can't afford our waits to timeout prematurely.
Discard jiffies and change to ktime to detect timeouts.

Reported-by: Imre Deak <imre.deak@intel.com>
References: https://lkml.org/lkml/2018/4/18/798 [1]
Cc: Imre Deak <imre.deak@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 8b20824e806e..ac7565220aa3 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -49,12 +49,12 @@
  * check the condition before the timeout.
  */
 #define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
-	unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;	\
+	const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
 	long wait__ = (Wmin); /* recommended min for usleep is 10 us */	\
 	int ret__;							\
 	might_sleep();							\
 	for (;;) {							\
-		bool expired__ = time_after(jiffies, timeout__);	\
+		const bool expired__ = ktime_after(ktime_get_raw(), end__); \
 		OP;							\
 		if (COND) {						\
 			ret__ = 0;					\
-- 
2.14.1

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^ permalink raw reply related	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2018-04-24 14:12 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-04-20  9:54 [PATCH] drm/i915: Use ktime on wait_for Mika Kuoppala
2018-04-20 10:23 ` Sagar Arun Kamble
2018-04-20 10:39   ` Chris Wilson
2018-04-20 11:55     ` Sagar Arun Kamble
2018-04-20 12:25     ` Mika Kuoppala
2018-04-20 10:27 ` Chris Wilson
2018-04-20 12:28   ` Imre Deak
2018-04-24 14:11     ` Mika Kuoppala
2018-04-20 11:41 ` ✓ Fi.CI.BAT: success for " Patchwork
2018-04-20 12:25 ` ✓ Fi.CI.IGT: " Patchwork

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