[Intel-gfx] [PATCH 07/23] drm/i915/gt: Move the [class][inst] lookup for engines onto the GT

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-07-26 10:22:08)
> 
> On 23/07/2019 19:38, Chris Wilson wrote:
> I read it, relatively rushed, since pressure keeps getting applied! :/
> 
> There are some good parts and implementation looks okay, but I am not 
> sure we need a tree. Nodes are bigger than pointers, management code is 
> bigger, lookup is slower.. is it a win all things considered?

A big win imo. Consider that this interface is purely debug, the primary
interface runtime will be via gt->engines, the nodes are much smaller
than the sparse array.

I am adamant that we are not adding more sparse arrays. A 2D lookup
table since that matches the HW, but even then we may just end up with
LUT (1 extra pointer load to replace the sparse array with a compact?)
-Chris