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

["Murthy, Arun R" <arun.r.murthy@gmail.com>]

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!

Thanks and Regards,
Arun R Murthy
-------------------