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

[Murthy, Arun R]

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.

Thanks and Regards,
Arun R Murthy
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