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.
And please stop conflating is_global_context when we have already a very
good expression for when the context is owned by no file.
-Chris
No existing code uses that as a test. And patch 1 of this set dropped
file_priv anyway, since there was no actual use for it anywhere at all!
This way we don't risk having dangling pointers to deallocated file objects.
.Dave.
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