When using PBOs to upload texture data, which call triggers the actual DMA operation?

[Marek Olšák]

On Sat, Aug 27, 2016 at 10:43 AM, Clemens Eisserer <linuxhippy at gmail.com> wrote:
> Hi Marek,
>
> Thanks a lot for the detailed explanation. I asked it here, because I
> was not sure whether the details I asked are driver specific.
>
>> All GPU operations are asynchronous and don't
>> cause any stalls on the CPU side.
>
> And what about GPU stalls? From what I read it seems currently DMA can
> not operate concurrently with the 3D engine, so would it be benefitial
> for upload performance to instead use SSBOs located in GTT accessed by
> a shader, so the 3D engine does perform the copy itself?

glTexSubImage2D with a PBO source is implemented by binding the PBO as
a texture buffer object and drawing into the texture. There is no DMA.

Marek