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

[Tvrtko Ursulin]

On 26/07/2019 10:33, Chris Wilson wrote:
> 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 guess it depends. One rb_node is three pointers and can only be used 
from a single tree. Nor does the patch replaces all sparse arrays.

> 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?)

I feel it's too early for this specific patch.

Regards,

Tvrtko