[PATCH 2/4] drm/amdkfd: Adding new IOCTL for scratch memory

[Alex Deucher]

On Tue, Aug 15, 2017 at 4:24 AM, Christian König
<deathsimple at vodafone.de> wrote:
> Am 14.08.2017 um 17:31 schrieb Felix Kuehling:
>>
>> [SNIP]
>> Repeating the same argument I made on another email:
>
>
> Commented on that in the other mail, let's keep the discussion on this topic
> there.
>
>>> BTW: What exactly this this good for?
>>
>> Scratch memory is private memory per work-item. It's used when a shader
>> program has too few registers available. With HSA we use flat scratch
>> addressing, where shaders can access private memory in a special scratch
>> aperture using normal memory instructions. Using the same virtual
>> address, each work item gets its own private piece of memory. The
>> hardware does the address translation from the VA in the private
>> aperture to a scratch-backing VA. The application is responsible for
>> allocating the memory to back that scratch area, and to map it somewhere
>> in its virtual address space.
>>
>> This ioctl tells the hardware (or HWS firmware) the VA of the scratch
>> backing memory.
>
>
> Ok, you've got me lost here. Not that I'm deeply into that stuff, but my
> last status is that those apertures are global and not per/process or VMID.
>
> That would mean that when two processes try to set two different addresses
> we are completely lost here.
>

The scratch and lds apertures are per vmid.  See gfx_v8_0_init_compute_vmid()

Alex