Re: [PATCH v4] drm/i915: use hrtimer in wait for vblank

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 01, 2014 at 10:14:12AM +0530, Murthy, Arun R wrote:
> On Thursday 27 March 2014 10:18 AM, Murthy, Arun R wrote:
> >On Tuesday 25 March 2014 03:16 PM, Murthy, Arun R wrote:
> >>On Tuesday 25 March 2014 03:02 PM, Jani Nikula wrote:
> >>>On Tue, 25 Mar 2014, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> >>>>On Tue, Mar 25, 2014 at 02:28:22PM +0530, Arun R Murthy wrote:
> >>>>>In wait for vblank use usleep_range, which will use hrtimers instead of
> >>>>>msleep. Using msleep(1~20) there are more chances of sleeping for 20ms.
> >>>>>Using usleep_range uses hrtimers and hence are precise, worst case will
> >>>>>trigger an interrupt at the higher/max timeout.
> >>>>>
> >>>>>As per kernel document "Documentation/timers/timers-howto.txt" sleeping
> >>>>>for 10us to 20ms its recomended to use usleep_range.
> >>>>>
> >>>>>Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> >>>>Lgtm, I still feel that our use of W=1 is fairly arbitrary and worth
> >>>>tweaking in future.
> >>>With the current code, this is essentially the same as the original
> >>>patch. We never have W > 20, and thus we always take the usleep_range()
> >>>path. So W is definitely worth tweaking if we go with this now.
> >>>
> >>>Nitpick, the macro params should be parenthesized. This will now break
> >>>for _wait_for(cond, 10, 2 + 1) and such.
> >>wait_for(COND, TIMEOUT, ATOMIC, MS)
> >>and remove all wait_for_X
> >>
> >>function will look like
> >>_wait_for(COND< TIMEOUT, ATOMIC, MS)
> >>{
> >>       /* loop */
> >>           /* check condition */
> >>           if (atomic)
> >>               cpu_relax()
> >>           else
> >>               if (ms > 20)
> >>                   msleep
> >>               else
> >>                   usleep_range
> >>}
> >>
> >>caller for wait_for will be setting all the parameters and hence no tweaks.
> >Any comments on this?
> Gentle reminder!

See my other mail somewhere in one your patch resends:

http://www.spinics.net/lists/intel-gfx/msg42439.html

If this is really just to optimize vblank waits we can do much better.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch