[QUESTION] sh_mem_bases: amdkfd vs amdgpu

[Felix Kuehling]

Am 2022-05-17 um 20:32 schrieb robert.dazi at yahoo.com:
> Hi,
>
> There is an interesting feature divergence between amdgpu and amdkfd concerning the shared/private apertures. I restricted my analysis to gfx9, it may differ with other gfx.
>
> In amdgpu, the pair of aperture start addresses is defined the following way (in gmc_v9_0.c):
>
> * shared_aperture_start = 0x2000000000000000ULL
> * private_aperture_start = 0x1000000000000000ULL
>
> In amdkfd, the pair is reversed (cf kfd_flat_memory.c and kfd_device_queue_manager_v9.c):
>
> * lds_base (ie shared_aperture_start) = (0x1UL) << 48
> * scratch_base (ie private_aperture_start) = (0x2UL) << 48

It's more than just reversed. If I counted 0s correctly, the aperture 
start addresses in gmc_v9_0.c expressed the same way would be

shared_aperture_start = 0x2ULL << 60;
private_aperture_start = 0x1ULL << 60;


>
> Is there any reason why those two definitions diverge ?

I don't think there is any deliberate reason for them to diverge. But 
there is also no reason for them to be the same. The sh_mem_bases 
register is per-VMID, which means these settings can be different for 
every address space. The address spaces for graphics and compute are 
defined independently of each other, and there was no reason to 
coordinate these settings.

Regards,
   Felix


>
> Thanks,
>
> RD