Re: [PATCH libdrm] libdrm_amdgpu: add kernel semaphore support

["Marek Olšák" <maraeo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Dave,

If you just add "get" functions for what you need from amdgpu objects,
that should be fine.

Marek

On Mon, Jul 17, 2017 at 11:00 PM, Dave Airlie <airlied@gmail.com> wrote:
> On 18 July 2017 at 03:02, Christian König <deathsimple@vodafone.de> wrote:
>> Am 17.07.2017 um 05:36 schrieb Dave Airlie:
>>>>
>>>> I can take a look at it, I just won't have time until next week most
>>>> likely.
>>>
>>> I've taken a look, and it's seemingly more complicated than I'm
>>> expecting I'd want to land in Mesa before 17.2 ships, I'd really
>>> prefer to just push the new libdrm_amdgpu api from this patch. If I
>>> have to port all the current radv code to the new API, I'll most
>>> definitely get something wrong.
>>>
>>> Adding the new API so far looks like
>>> https://cgit.freedesktop.org/~airlied/drm/log/?h=drm-amdgpu-cs-submit-raw
>>>
>>>
>>> https://cgit.freedesktop.org/~airlied/drm/commit/?h=drm-amdgpu-cs-submit-raw&id=e7f85d0ca617fa41e72624780c9035df132e23c4
>>> being the API, and whether it should take a uint32_t context id or
>>> context handle left as an open question in the last patch in the
>>> series.
>>
>>
>> I would stick with the context handle, as far as I can see there isn't any
>> value in using the uint32_t for this.
>>
>> We just want to be able to send arbitrary chunks down into the kernel
>> without libdrm_amdgpu involvement and/or the associated overhead of the
>> extra loop and the semaphore handling.
>>
>> So your "amdgpu/cs: add new raw cs submission interface just taking chunks"
>> patch looks fine to me as far as I can tell.
>>
>> As far as I can see the "amdgpu: refactor semaphore handling" patch is
>> actually incorrect. We must hole the mutex while sending the CS down to the
>> kernel, or otherwise "context->last_seq" won't be accurate.
>>
>>> However to hook this into radv or radeonsi will take a bit of
>>> rewriting of a lot of code that is probably a bit more fragile than
>>> I'd like for this sort of surgery at this point.
>>
>>
>> Again, I can move over the existing Mesa stuff if you like.
>>
>>> I'd actually suspect if we do want to proceed with this type of
>>> interface, we might be better doing it all in common mesa code, and
>>> maybe bypassing libdrm_amdgpu altogether, which I suppose the API I've
>>> written here is mostly already doing.
>>
>>
>> I want to stick with the other interfaces for now. No need to make it more
>> complicated than it already is.
>>
>> Only the CS stuff is the most performance critical and thing we have right
>> now.
>
> As I suspected this plan is full of traps.
>
> So with the raw cs api I posted (using amdgpu_bo_list_handle instead), I ran
> into two places the abstraction cuts me.
>
>   CC       winsys/amdgpu/radv_amdgpu_cs.lo
> winsys/amdgpu/radv_amdgpu_cs.c: In function ‘radv_amdgpu_cs_submit’:
> winsys/amdgpu/radv_amdgpu_cs.c:1173:63: error: dereferencing pointer
> to incomplete type ‘struct amdgpu_bo’
>    chunk_data[i].fence_data.handle = request->fence_info.handle->handle;
>                                                                ^~
> winsys/amdgpu/radv_amdgpu_cs.c:1193:31: error: dereferencing pointer
> to incomplete type ‘struct amdgpu_context’
>     dep->ctx_id = info->context->id;
>
> In order to do user fence chunk I need the actual bo handle not the
> amdgpu wrapped one, we don't have an accessor method for that.
>
> In order to do the dependencies chunks, I need a context id.
>
> Now I suppose I can add chunk creation helpers to libdrm, but it does
> seems like it breaks the future proof interface if we can't access the
> details of a bunch of objects we want to pass through to the kernel
> API.
>
> Dave.
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