[PATCH libdrm] drm/amdgpu: add new low overhead command submission API. (v2)

[Christian König]

Am 10.08.2017 um 21:43 schrieb Dave Airlie:
> On 10 August 2017 at 23:56, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>> Hi Dave,
>>
>> On 18 July 2017 at 04:52, Dave Airlie <airlied at gmail.com> wrote:
>>
>>> +int amdgpu_cs_submit_raw(amdgpu_device_handle dev,
>>> +                        amdgpu_context_handle context,
>>> +                        amdgpu_bo_list_handle bo_list_handle,
>>> +                        int num_chunks,
>>> +                        struct drm_amdgpu_cs_chunk *chunks,
>>> +                        uint64_t *seq_no)
>>> +{
>>> +       union drm_amdgpu_cs cs = {0};
>>> +       uint64_t *chunk_array;
>>> +       int i, r;
>>> +       if (num_chunks == 0)
>>> +               return -EINVAL;
>>> +
>>> +       chunk_array = alloca(sizeof(uint64_t) * num_chunks);
>> Out of curiosity:
>> Does malloc/free produce noticeable overhead that lead you you alloca?
> The preexisting code for these ioctls used alloca so I just followed
> the existing pattern.
>
> I doubt we'd notice malloc/free, but we shouldn't also be sending more
> than 5-10 chunks
> even in the future, so stack alloc should be fine.
>
>> num_chunks is signed - should we bail on negative values, can we make
>> it unsigned?
> Possibly, I don't see random users of this API appearing though, but yeah could
> change the if <= 0.

I would rather make the variable unsigned, but yeah it's not so much of 
an issue.

Christian.

>
> Dave.
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