[Nouveau] [RFC PATCH 0/5] More explicit pushbuf error handling

[Konsta Hölttä]

Hi there,

These patches work as a starting point for more explicit error mechanisms and
better robustness. At the moment, when a job hangs or faults, it seems that
nouveau doesn't quite know how to handle the situation and often results in a
hang. Some of these situations would require either completely resetting the
gpu, or a more complex path for only recovering the faulted channel.

To start, I worked on support for letting userspace know what exactly happened.
Proper recovery would come later. The "error notifier" in the first patch is a
simple shared buffer between kernel and userspace. Its error codes match
nvgpu's. Alternatively, the status could be queried with an ioctl, but that
would be considerably more heavyweight. I'd like to know if the event mechanism
is meant for these kinds of events at all (engines notify errors upwards to the
drm layer). Another alternative would probably be to register the same buffer
to all necessary engines separately in method calls? Or register it to just one
(e.g., fifo) and get that engine somehow when errors happen in others? Please
comment on this; I wrote this before understanding the mthd mechanism.

Additionally, priority and timeout management for separate channels in flight
is added in two patches. Neither is exactly what the name says, but the effect
should be the same, and this is what nvgpu does currently. Those two patches
call the fifo channel object's methods directly from userspace, so a hack is
added in the nvif path to accept that. The objects are NEW'd from kernel space,
so calling from userspace isn't allowed, as it appears. How should this be
handled?

Also, since nouveau often hangs on errors, the userspace hangs too (waiting on
a fence). The final patch attempts to fix this in a couple of specific error
paths to forcibly update all fences to be finished. I'd like to hear how that
would be handled properly - consider the patch just a proof-of-concept and
sample of what would be necessary, supporting this question of mine again.

I don't expect the patches to be accepted as-is - as a newbie, I'd appreciate
any high-level comments on if I've understood anything, especially the event
and nvif/method mechanisms (I use the latter from userspace with a hack
constructed from the perfmon branch seen here earlier into nvidia's internal
libdrm-equivalent). The fence-forcing thing is something that is necessary with
the error notifiers (at least with our userspace that waits really long or
infinitely on fences). I'm working specifically on Tegra and don't know much
about the desktop's userspace details, so I may be biased in some areas.

I'd be happy to write sample tests on e.g. libdrm for the new methods once the
kernel patches would get to a good shape, if that's required for accepting new
features. I tested these to work as a proof-of-concept on Jetson TK1, and the
code is adapted from the latest nvgpu.

The patches can also be found in http://github.com/sooda/nouveau and are based
on a version of gnurou/staging.

Thanks!
Konsta (sooda in IRC)

Konsta Hölttä (5):
  notify channel errors to userspace
  HACK don't verify route == owner in nvkm ioctl
  gk104: channel priority/timeslice support
  channel timeout using repeated sched timeouts
  force fences updated in error conditions

 drm/nouveau/include/nvif/class.h       |  20 +++++
 drm/nouveau/include/nvif/event.h       |  12 +++
 drm/nouveau/include/nvkm/engine/fifo.h |   5 +-
 drm/nouveau/nouveau_chan.c             |  54 ++++++++++++
 drm/nouveau/nouveau_chan.h             |   5 ++
 drm/nouveau/nouveau_drm.c              |   1 +
 drm/nouveau/nouveau_fence.c            |  13 +--
 drm/nouveau/nouveau_gem.c              |  50 +++++++++++
 drm/nouveau/nouveau_gem.h              |   2 +
 drm/nouveau/nvkm/core/ioctl.c          |   5 +-
 drm/nouveau/nvkm/engine/fifo/base.c    |  57 ++++++++++++-
 drm/nouveau/nvkm/engine/fifo/gf100.c   |   2 +-
 drm/nouveau/nvkm/engine/fifo/gk104.c   | 150 +++++++++++++++++++++++++++++++--
 drm/nouveau/nvkm/engine/fifo/nv04.c    |   2 +-
 drm/nouveau/nvkm/engine/gr/gf100.c     |   4 +
 drm/nouveau/uapi/drm/nouveau_drm.h     |  12 +++
 16 files changed, 374 insertions(+), 20 deletions(-)

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2.1.4