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

[Daniel, Thomas]

> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel
> Vetter
> Sent: Monday, November 03, 2014 4:54 PM
> To: Daniel, Thomas
> Cc: intel-gfx at lists.freedesktop.org; shuang.he at linux.intel.com
> Subject: Re: [Intel-gfx] [PATCH 3/4] drm/i915/bdw: Pin the context backing
> objects to GGTT on-demand
> 
> 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?
This is a rebase and bug fix of the original patch to unblock execlists
enabling.  Plan is to address the rest of the issues after the big
seqno->request rearchitecting change goes in.

Thomas.

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch