Re: [PATCH] drm/i915: use hrtimer in wait for vblank

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Mar 24, 2014 at 09:34:35AM +0000, Murthy, Arun R wrote:
> >> diff --git a/drivers/gpu/drm/i915/intel_drv.h 
> >> b/drivers/gpu/drm/i915/intel_drv.h
> >> index 44067bc..079280a 100644
> >> --- a/drivers/gpu/drm/i915/intel_drv.h
> >> +++ b/drivers/gpu/drm/i915/intel_drv.h
> >> @@ -52,7 +52,7 @@
> >>  			break;						\
> >>  		}							\
> >>  		if (W && drm_can_sleep())  {				\
> >> -			msleep(W);					\
> >> +			usleep_range(W * 1000, W * 2 * 1000);		\
> >>  		} else {						\
> >>  			cpu_relax();					\
> >>  		}							\
> >
> > Ok. But W is still just a random value we picked for being the mininum 
> > legal value for msleep(). So just usleep_range(500, 2000) or somesuch 
> > will be fine. We can rename W to CAN_SLEEP it that helps.
> 
> We do use _wait_for directly from intel_dp.c with W == 10 to not retry so many times on what's expected to be a long wait.
> 
> Its not expected to be too long, we tend to get vblank every 16ms.  With using usleep_range
> with min and max as 1-2ms, we have observed that this function consuming 4ms to 17ms.
> Having 10ms sleep timer, we might tend to be blocking for 6ms in some cases.(from the above data)
> Moreover 10ms usleep doesn't guarantee that we get a chance to execute after 10ms, it might
> get increased due to scheduling. So ideal solution would be to use useep_range which uses hrtimers.

Can you please do proper quoting when replying? It makes it fairly hard to
figure out what's your response when you reply in-line, especially in more
complicated threads. And top-posting isn't an option either, especially
for more in-depth discussions where the different issues need to be
treated as separate points.

You need a real mail client for this, Outlook won't cut it. Jesse is
floating slides internal with all the details and tons of links to
resources.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch