"Fixes" for page flipping under PRIME on AMD & nouveau

[Marek Olšák]

On Thu, Aug 18, 2016 at 4:23 AM, Michel Dänzer <michel at daenzer.net> wrote:
> Maybe the rasterization as two triangles results in bad PCIe bandwidth
> utilization. Using the asynchronous DMA engine for these transfers would
> probably be ideal, but having the 3D engine rasterize a single rectangle
> (either using the rectangle primitive or a large triangle with scissor)
> might already help.

There is only one thing that's bad for PCIe when the surface is
linear: the 3D engine. Disabling all but the first shader engine and
all but the first 2 RBs should improve performance for blits from VRAM
to GTT. The closed driver does that, but I don't remember if the
destination must be linear, must be in GTT, or both. In any case, SDMA
should still be the best for VRAM->GTT blits.

Marek