[Intel-gfx] [PATCH 3/4] drm/i915/bdw: Pin the context backing objects to GGTT on-demand

[Daniel Vetter]

On Wed, Oct 29, 2014 at 09:52:52AM +0000, Thomas Daniel wrote:
> From: Oscar Mateo <oscar.mateo at intel.com>
> 
> Up until now, we have pinned every logical ring context backing object
> during creation, and left it pinned until destruction. This made my life
> easier, but it's a harmful thing to do, because we cause fragmentation
> of the GGTT (and, eventually, we would run out of space).
> 
> This patch makes the pinning on-demand: the backing objects of the two
> contexts that are written to the ELSP are pinned right before submission
> and unpinned once the hardware is done with them. The only context that
> is still pinned regardless is the global default one, so that the HWS can
> still be accessed in the same way (ring->status_page).
> 
> v2: In the early version of this patch, we were pinning the context as
> we put it into the ELSP: on the one hand, this is very efficient because
> only a maximum two contexts are pinned at any given time, but on the other
> hand, we cannot really pin in interrupt time :(
> 
> v3: Use a mutex rather than atomic_t to protect pin count to avoid races.
> Do not unpin default context in free_request.
> 
> v4: Break out pin and unpin into functions.  Fix style problems reported
> by checkpatch
> 
> Issue: VIZ-4277

This doesn't really do the full task since the integration with the
shrinker and related igt testcases are missing. What's your plane here?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch