[Nouveau] CUDA fixed VA allocations and sparse mappings

[C Bergström]

On Wed, Jul 8, 2015 at 6:58 AM, Ben Skeggs <skeggsb at gmail.com> wrote:
> 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* :)

I'm not sure I follow exactly what you mean, but I think the answer is
- don't setup the graphics engine if you're in "compute" mode. Doing
that, iiuc, will at least provide a start to support for compute.
Anyone who argues that graphics+compute is critical to have working at
the same time is probably a 1%.