[Intel-gfx] [PATCH v4] drm/i915: use hrtimer in wait for vblank

[Murthy, Arun R]

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 at 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 at 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?

Thanks and Regards,
Arun R Murthy
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