[PATCH 1/3] dma-fence: Reserve 0 as a special NO_CONTEXT token

[Christian König]

Am 08.04.2017 um 20:00 schrieb Chris Wilson:
> On Sat, Apr 08, 2017 at 07:49:37PM +0200, Christian König wrote:
>> Am 08.04.2017 um 18:26 schrieb Chris Wilson:
>>> Reserve 0 for general use a token meaning that the fence doesn't belong
>>> to an ordered timeline (fence context).
>> NAK, we kept context allocation cheap to avoid exactly that.
> However, they result in very sparse mappings.

Which is perfectly fine at least for how we use this in Radeon and Amdgpu.

The fence context is used as key for a hashtable, even when the context 
is only used once we want an evenly distribution over all of them.

>
>> Please elaborate further why it should be necessary now.
> Because I want to efficiently exclude them from comparisons as
> demonstrated by this small series as there may be several hundred such
> fences as dependencies for this job.

That would horrible break Amdgpu, Radeon and the GPU scheduler because 
all of them assume that context numbers are unique.

So that is a clear NAK from my side,
Christian.

> -Chris
>