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

[Jani Nikula <jani.nikula@linux.intel.com>]

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.

Arun, please don't immediately reply with updated patches if there's
discussion still going on. See what the conclusion is first. Thanks.

BR,
Jani.




>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre

-- 
Jani Nikula, Intel Open Source Technology Center