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

Chris Wilson chris at chris-wilson.co.uk
Wed Jun 18 18:34:49 CEST 2014

On Wed, Jun 18, 2014 at 05:16:03PM +0100, oscar.mateo at intel.com wrote:
> From: Oscar Mateo <oscar.mateo at intel.com>
> The original comment that introduced it said:
> commit 0009e46cd54324c4af20b0b52b89973b1b914167
> Author: Ben Widawsky <ben at 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 at intel.com>

I have sent the very same patch, so
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Chris Wilson, Intel Open Source Technology Centre

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