Nouveau - Dec 2016 - 4.9-rc7 nouveau fails on arm64 64k page kernel but works with 4k

On 07/12/16 06:39 PM, Alexandre Courbot wrote:
> On Fri, Dec 2, 2016 at 12:23 PM, Ilia Mirkin <imirkin at
alum.mit.edu> wrote:
>> That's right -- nouveau currently requires 4k page sizes to work.
This is a
>> software limitation, not a hardware one though.
> 
> Looking at the trace I wonder - is the limitation in Nouveau or in TTM?
Nouveau. Non-4K page sizes work fine with radeon (and presumably amdgpu).


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer

On Wed, Dec 7, 2016 at 6:53 PM, Michel Dänzer <michel at daenzer.net>
wrote:
> On 07/12/16 06:39 PM, Alexandre Courbot wrote:
>> On Fri, Dec 2, 2016 at 12:23 PM, Ilia Mirkin <imirkin at
alum.mit.edu> wrote:
>>> That's right -- nouveau currently requires 4k page sizes to
work. This is a
>>> software limitation, not a hardware one though.
>>
>> Looking at the trace I wonder - is the limitation in Nouveau or in TTM?
>
> Nouveau. Non-4K page sizes work fine with radeon (and presumably amdgpu).
Thanks for the precision. I will check if Tegra iGPUs are also
affected by this - if they are then it gives me a good excuse to take
care of this bug.

On Wed, Dec 7, 2016 at 4:57 AM, Alexandre Courbot <gnurou at gmail.com>
wrote:
> On Wed, Dec 7, 2016 at 6:53 PM, Michel Dänzer <michel at daenzer.net>
wrote:
>> On 07/12/16 06:39 PM, Alexandre Courbot wrote:
>>> On Fri, Dec 2, 2016 at 12:23 PM, Ilia Mirkin <imirkin at
alum.mit.edu> wrote:
>>>> That's right -- nouveau currently requires 4k page sizes to
work. This is a
>>>> software limitation, not a hardware one though.
>>>
>>> Looking at the trace I wonder - is the limitation in Nouveau or in
TTM?
>>
>> Nouveau. Non-4K page sizes work fine with radeon (and presumably
amdgpu).
>
> Thanks for the precision. I will check if Tegra iGPUs are also
> affected by this - if they are then it gives me a good excuse to take
> care of this bug.
For the most part it's confusion in the (nouveau) code as to what's a
gpu page and what's a cpu page (and the shifts involved). There are
some fringe issues that will need to be addressed, like the fact that
it's no longer a 1:1 mapping, which might be assumed in some places.

However I thought that 64K-pages were frowned upon nowadays for the
kernel - outside of HPC loads, most of the kernel memory becomes
pagecache, and files don't tend to be 64K-sized, so you have tons of
wasted memory (since you never cache multiple files in the same page).

But don't take that as me disapproving of such a project. It'd esp be
nice to do something like this outside of the PPC64 environment, where
BE concerns mix in with the 64K page concerns, and nothing works as a
result.

  -ilia

On 12/07/2016 07:57 PM, Alexandre Courbot wrote:
> On Wed, Dec 7, 2016 at 6:53 PM, Michel Dänzer <michel at daenzer.net>
wrote:
>> On 07/12/16 06:39 PM, Alexandre Courbot wrote:
>>> On Fri, Dec 2, 2016 at 12:23 PM, Ilia Mirkin <imirkin at
alum.mit.edu> wrote:
>>>> That's right -- nouveau currently requires 4k page sizes to
work. This is a
>>>> software limitation, not a hardware one though.
>>>
>>> Looking at the trace I wonder - is the limitation in Nouveau or in
TTM?
>>
>> Nouveau. Non-4K page sizes work fine with radeon (and presumably
amdgpu).
> 
> Thanks for the precision. I will check if Tegra iGPUs are also
> affected by this - if they are then it gives me a good excuse to take
> care of this bug.
I *should* have this fixed with a large chunk of MMU work I have pending
(I had to drop it temporarily to work on atomic/mst support, but it'll
be picked up, rebased, and finished in the near future).  I haven't
actually tested on 64KiB pages yet, but, I plan to before releasing it.
> _______________________________________________
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> Nouveau at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/nouveau
> 
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