[Intel-gfx] [PATCH v2, 2/4] drm/i915: simplify testing for the global default context

Chris Wilson chris at chris-wilson.co.uk
Mon Jan 4 11:39:20 PST 2016

On Mon, Jan 04, 2016 at 05:43:10PM +0000, Dave Gordon wrote:
> On 23/12/15 21:02, Chris Wilson wrote:
> >On Wed, Dec 23, 2015 at 07:33:53PM +0000, Dave Gordon wrote:
> >>There are quite a number of places where the driver tests whether
> >>a given context is or is not the global default context, usually by
> >>checking whether an engine's default_pointer points to the context.
> >>Now that we have a 'is_global_default' flag in the context itself,
> >>all these tests these can be rewritten to use it. This makes the
> >>logic more obvious, and usually saves at least one memory reference.
> >>In addition, with these uses eliminated, a future patch will be able
> >>to get rid of engine::default_context entirely.
> >
> >All the execlists use of ctx != ring->default_context stems from a
> >misstep in execlists - if you stop treating that default_context as
> >special during request processing and just take the pin/unpin at
> >init/fini of the ring, they all disappear.
> We do already pin/unpin the default context at creation/deletion;
> AFAICS the extra tests are probably an attempt not to do an extra
> pin/unpin on an object which is by definition already pinned. And
> I'd be quite happy to get rid of those tests, and just issue a pin
> for *every* request issues on a context -- indeed, I think Nick may
> have just such a patch. But his changes are blocked on getting the
> elimination of ring->default_context (patch 4 of THIS set) merged
> first, since having those backpointers dictates the order of
> creation and destruction.

This series is NAKed.

Chris Wilson, Intel Open Source Technology Centre

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