[Nouveau] CUDA fixed VA allocations and sparse mappings

[Ben Skeggs]

On 8 July 2015 at 09:53, C Bergström <cbergstrom at pathscale.com> wrote:
> regarding
> --------
> Fixed address allocations weren't going to be part of that, but I see
> that it makes sense for a variety of use cases.  One question I have
> here is how this is intended to work where the RM needs to make some
> of these allocations itself (for graphics context mapping, etc), how
> should potential conflicts with user mappings be handled?
> --------
> As an initial implemetation you can probably assume that the GPU
> offloading is in "exclusive" mode. Basically that the CUDA or OpenACC
> code has full ownership of the card. The Tesla cards don't even have a
> video out on them. To complicate this even more - some offloading code
> has very long running kernels and even worse - may critically depend
> on using the full available GPU ram. (Large matrix sizes and soon big
> Fortran arrays or complex data types)
This doesn't change that, to setup the graphics engine, the driver
needs to map various system-use data structures into the channel's
address space *somewhere* :)

>
> Long term - direct PCIe copies between cards will be important.. aka
> zero-copy. It may seem crazy, but when you have 16+ GPU in a single
> workstation (Cirrascale) stuff like this is key.