Re: [PATCH v2 08/12] drm/amdgpu: use doorbell manager for kfd kernel doorbells

[Felix Kuehling <felix.kuehling@amd.com>]

On 2023-04-25 15:59, Shashank Sharma wrote:
>
> On 24/04/2023 21:56, Felix Kuehling wrote:
>> On 2023-04-22 2:39, Shashank Sharma wrote:
>>> - KFD process level doorbells: doorbell pages which are allocated by 
>>> kernel but mapped and written by userspace processes, saved in 
>>> struct pdd->qpd->doorbells
>>>
>>> size = kfd_doorbell_process_slice.
>>>
>>> We realized that we only need 1-2 doorbells for KFD kernel level 
>>> stuff (so kept it one page), but need 2-page of doorbells for KFD 
>>> process, so they are sized accordingly.
>>>
>>> We have also run kfd_test_suit and verified the changes for any 
>>> regression. Hope this helps in explaining the design.
>>
>> Right, I missed that this was only for kernel doorbells. I wonder 
>> whether KFD really needs its own page here. I think we only need a 
>> doorbell for HWS. And when we use MES, I think even that isn't needed 
>> because MES packet submissions go through amdgpu. So maybe KFD 
>> doesn't need its own kernel-mode doorbell page any more on systems 
>> with user graphics mode queues.
>
> Yeah, for any IP with MES enabled, KFD doesn't need kernel level 
> doorbells. But I still allocated a page just to make sure we do not 
> break any non-MES platforms or use cases where MES is deliberately 
> disabled from kernel command line. Hope that works for you.

Even without MES, we still only need one doorbell for HWS. Allocating a 
whole page for that is wasteful. Anyway, I'm OK with cleaning that up later.

Regards,
   Felix


>
> - Shashank
>
>>
>> Regards,
>>   Felix
>>
>>
>>>
>>> - Shashank