Re: [PATCH] drm/i915: Remove ctx->last_ring

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jun 18, 2014 at 05:34:49PM +0100, Chris Wilson wrote:
> On Wed, Jun 18, 2014 at 05:16:03PM +0100, oscar.mateo@intel.com wrote:
> > From: Oscar Mateo <oscar.mateo@intel.com>
> > 
> > The original comment that introduced it said:
> > 
> > commit 0009e46cd54324c4af20b0b52b89973b1b914167
> > Author: Ben Widawsky <ben@bwidawsk.net>
> > Date:   Fri Dec 6 14:11:02 2013 -0800
> > 
> >     drm/i915: Track which ring a context ran on
> > 
> >     Previously we dropped the association of a context to a ring. It is
> >     however very important to know which ring a context ran on (we could
> >     have reused the other member, but I was nitpicky).
> > 
> >     This is very important when we switch address spaces, which unlike
> >     context objects, do change per ring.
> > 
> >     As an example, if we have:
> > 
> >             RCS   BCS
> >     ctx            A
> >     ctx      A
> >     ctx      B
> >     ctx            B
> > 
> >     Without tracking the last ring B ran on, we wouldn't know to switch the
> >     address space on BCS in the last row.
> > 
> > But this is not really true, because we are already checking to != from (with
> > "from" being = ring->last_context) and that should be enough to make sure we
> > switch to the right address space.
> > 
> > We would have a problem if we switched the context object for every ring (since
> > then we would fail to do it in some situations) but we only switch it for the
> > render ring, so we don't care.
> > 
> > Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
> 
> I have sent the very same patch, so
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch