[Intel-gfx] [PATCH v2 06/11] drm/i915/scheduler: Record all dependencies upon request construction

[Chris Wilson]

On Mon, Nov 07, 2016 at 01:59:45PM +0000, Chris Wilson wrote:
> The scheduler needs to know the dependencies of each request for the
> lifetime of the request, as it may choose to reschedule the requests at
> any time and must ensure the dependency tree is not broken. This is in
> additional to using the fence to only allow execution after all
> dependencies have been completed.
> 
> One option was to extend the fence to support the bidirectional
> dependency tracking required by the scheduler. However the mismatch in
> lifetimes between the submit fence and the request essentially meant
> that we had to build a completely separate struct (and we could not
> simply reuse the existing waitqueue in the fence for one half of the
> dependency tracking). The extra dependency tracking simply did not mesh
> well with the fence, and keeping it separate both keeps the fence
> implementation simpler and allows us to extend the dependency tracking
> into a priority tree (whilst maintaining support for reordering the
> tree).
> 
> To avoid the additional allocations and list manipulations, the use of
> the priotree is disabled when there are no schedulers to use it.
> 
> v2: Create a dedicated slab for i915_dependency.
>     Rename the lists.

Sod. I've squashed the priority sort into this as a rebase calamity.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre