3.18-rc regression: drm/nouveau: use shared fences for readable objects

[Michael Marineau]

On Wed, Nov 19, 2014 at 12:10 AM, Maarten Lankhorst
<maarten.lankhorst at canonical.com> wrote:
> Hey,
>
> On 19-11-14 07:43, Michael Marineau wrote:
>> On 3.18-rc kernel's I have been intermittently experiencing GPU
>> lockups shortly after startup, accompanied with one or both of the
>> following errors:
>>
>> nouveau E[   PFIFO][0000:01:00.0] read fault at 0x000734a000 [PTE]
>> from PBDMA0/HOST_CPU on channel 0x007faa3000 [unknown]
>> nouveau E[     DRM] GPU lockup - switching to software fbcon
>>
>> I was able to trace the issue with bisect to commit
>> 809e9447b92ffe1346b2d6ec390e212d5307f61c "drm/nouveau: use shared
>> fences for readable objects". The lockups appear to have cleared up
>> since reverting that and a few related followup commits:
>>
>> 809e9447: "drm/nouveau: use shared fences for readable objects"
>> 055dffdf: "drm/nouveau: bump driver patchlevel to 1.2.1"
>> e3be4c23: "drm/nouveau: specify if interruptible wait is desired in
>> nouveau_fence_sync"
>> 15a996bb: "drm/nouveau: assign fence_chan->name correctly"
>
> Weird. I'm not sure yet what causes it.
>
> http://cgit.freedesktop.org/~mlankhorst/linux/commit/?h=fixed-fences-for-bisect&id=86be4f216bbb9ea3339843a5658d4c21162c7ee2

Building a kernel from that commit gives me an entirely new behavior:
X hangs for at least 10-20 seconds at a time with brief moments of
responsiveness before hanging again while gitk on the kernel repo
loads. Otherwise the system is responsive. The head of that
fixed-fences-for-bisect branch (1c6aafb5) which is the "use shared
fences for readable objects" commit I originally bisected to does
feature the complete lockups I was seeing before.

>
> On the EDITED patch from fixed-fences-for-bisect, can you do the following:
>
> In nouveau/nv84_fence.c function nv84_fence_context_new, remove
>
> fctx->base.sequence = nv84_fence_read(chan);
>
> and add back
>
> nouveau_bo_wr32(priv->bo, chan->chid * 16/4, 0x00000000);

Making your suggested change on top of each 86be4f21 and 1c6aafb5 made
no noticeable difference in either of the two behaviors.

>
> If that fails you should compile your kernel with trace events, to get some debugging info from the fences. I'll post debugging info if this does not fix it.

Happy to gather whatever debug log or tracing data you need :)

-- 
Michael Marineau