There are too many oustanding issues:
- Fence handling in the current code is broken. There's a patch series
from me, but it's blocked on and extended review (which includes
writing the testcases).
- IOMMU mapping handling is broken, we need to properly refcount it -
currently it gets destroyed when the first vma is unbound, so way
too early.
- There's a pending reset issue on snb. Since Mika's reset work and
full ppgtt have been pulled in in separate branches and ended up
intermittingly breaking each another it's unclear who's the exact
culprit here.
- We still have persistent evidince of crazy recursion bugs through
vma_unbind and ppgtt_relase, e.g.
https://bugs.freedesktop.org/show_bug.cgi?id=73383
This issue (and a few others meanwhile resolved) have blocked our
performance measuring/tuning group since 3 months.
- Secure batch dispatching is broken. This is blocking Brad Volkin's
command checker work since 3 months.
All these issues are confirmed to only happen when full ppgtt is
enabled, falling back to aliasing ppgtt resolves them. But even
aliasing ppgtt itself still has a regression:
- We currently unconditionally bind objects into the aliasing ppgtt,
which means all priviledged objects like ringbuffers are visible to
unpriviledged access again. On top of that this also breaks the
command checker for aliasing ppgtt, since it can't hide the
validated batch any more.
Furthermore topic/full-ppgtt has never been reviewed:
- Lifetime rules around vma unbinding/release are unclear, resulting
into this awesome hack called ppgtt_release. Which seems to take the
blame for most of the recursion fallout.
- Context/ring init works different on gpu reset than anywhere else.
Such differeneces have in the past always lead to really hard to
track down bugs.
- Aliasing ppgtt is treated in a bunch of places as a real address
space, but it isn't - the real address space is always the global
gtt in that case. This results in a bit a mess between contexts and
ppgtt object, further complication the context/ppgtt/vma lifetime
rules.
- We don't have any docs describing the overall concepts introduced
with full ppgtt. A short, concise overview describing vmas and some
of the strange bits around them (like the unbound vmas used by
execbuf, or the new binding rules) really is needed.
Note that a lot of the post topic/full-ppgtt merge fallout has already
been addressed, this entire list here of 10 issues really only contains
the still outstanding issues.
Finally the 3.15 merge window is approaching and I think we need to
use the remaining time to ensure that our fallback option of using
aliasing ppgtt is in solid shape. Hence I think it's time to throw the
switch. While at it demote the helper from static inline status
because really.
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
93a25a9e2d