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

[Mario Kleiner]

On 08/18/2016 09:21 PM, Marek Olšák wrote:
> 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
>

Friday evening education question:

So if you have multiple render backends active they compete for PCIe bus 
access and some kind of "trashing" happens in the arbitration, 
drastically reducing the bandwidth?

thanks,
-mario