PRT support for amdgpu

[Christian König]

Am 31.01.2017 um 17:09 schrieb Alex Deucher:
> On Mon, Jan 30, 2017 at 7:57 AM, Christian König
> <deathsimple at vodafone.de> wrote:
>> Hi Dave and Bas,
>>
>> Hi Dave and Bas,
>>
>> the following set of patches is a proposal for adding support for partial resident textures (PRT) to the amdgpu kernel module.
>>
>> The basic idea behind PRT support is that you turn of VM fault reporting and only map parts of a texture into your virtual address space.
>>
>> When a shader now tries to sample from a not present page it gets a notification instead of a VM fault and can react gracefully by switch to a different LOD for example.
> Do we actually need to disable faults?  I guess the shader hw probably
> requires it to get the proper result in the shader?

Yes, you need to disable the VM faults for the PRT range otherwise the 
interrupt ring will just be flooded with faults.

Keep in mind that faults (or rather NACKs from the MC) are considered 
normal with that approach. This is also the reason why we need to change 
the TLB rules and also keep invalid entries in there.

Regards,
Christian.

>
> Alex
>
>> On our current available hardware generation you can unfortunately only turn of VM faults globally, but on future generation you can do this on a per page basis. So my proposal is to have a consistent interface over all generations with a per mapping PRT flag, but enable/disable it globally on current hardware when the first/last mapping is made/destroyed.
>>
>> An open problem with the proposal is that we don't know when or if we want to add the userspace implementation into radeonsi.
>>
>> So price question could you guys use this for radv as well? Or is it sufficient to just write an unit test for it?
>>
>> Best regards,
>> Christian.
>>
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