[Nouveau] CUDA fixed VA allocations and sparse mappings

[Ilia Mirkin]

On Tue, Jul 7, 2015 at 8:11 PM, C Bergström <cbergstrom at pathscale.com> wrote:
> On Wed, Jul 8, 2015 at 7:08 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> On Tue, Jul 7, 2015 at 8:07 PM, C Bergström <cbergstrom at pathscale.com> wrote:
>>> 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%.
>>
>> On NVIDIA GPUs, compute _is_ part of the graphics engine... aka PGRAPH.
>
> You can afaik setup PGRAPH without mapping memory for graphics. You
> just init the engine and get out of the way.

But... you need to map memory to set up the engine. Not a lot, but
it's gotta go *somewhere*.