[PATCH] drm: Defer disabling the vblank IRQ until the next interrupt (for instant-off)

[Michel Dänzer]

On 02.04.2015 20:34, Chris Wilson wrote:
> On vblank instant-off systems, we can get into a situation where the cost
> of enabling and disabling the vblank IRQ around a drmWaitVblank query
> dominates. However, we know that if the user wants the current vblank
> counter, they are also very likely to immediately queue a vblank wait
> and so we can keep the interrupt around and only turn it off if we have
> no further vblank requests in the interrupt interval.
> 
> After vblank event delivery there is a shadow of one vblank where the
> interrupt is kept alive for the user to query and queue another vblank
> event. Similarly, if the user is using blocking drmWaitVblanks, the
> interrupt will be disabled on the IRQ following the wait completion.
> However, if the user is simply querying the current vblank counter and
> timestamp, the interrupt will be disabled after every IRQ and the user
> will enabled it again on the first query following the IRQ.

As I mentioned before, it might not be too hard to make querying the
current counter work without enabling the interrupt. But this looks like
a step in the right direction.

Acked-by: Michel Dänzer <michel.daenzer at amd.com>


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer