On 11/21/2012 02:12 PM, Maarten Lankhorst wrote:
Op 21-11-12 13:42, Thomas Hellstrom schreef:
On 11/21/2012 12:38 PM, Maarten Lankhorst wrote:
Hey,
Op 20-11-12 16:08, Thomas Hellstrom schreef:
On 11/20/2012 02:13 PM, Maarten Lankhorst wrote:
Op 20-11-12 13:03, Thomas Hellstrom schreef:
On 11/20/2012 12:33 PM, Maarten Lankhorst wrote:
Op 20-11-12 08:48, Thomas Hellstrom schreef:
On 11/19/2012 04:33 PM, Maarten Lankhorst wrote:
Op 19-11-12 16:04, Thomas Hellstrom schreef:
On 11/19/2012 03:17 PM, Thomas Hellstrom wrote:
Hi,
This patch looks mostly good, although I think ttm_bo_cleanup_refs becomes
overly complicated:
Could this do, or am I missing something?
Actually, my version is bad, because ttm_bo_wait() is called with the lru lock
held.
/Thomas
Oh digging through it made me remember why I had to release the reservation
early and
had to allow move_notify to be called without reservation.
Fortunately move_notify has a NULL parameter, which is the only time that
happens,
so you can still check do BUG_ON(mem != NULL && !ttm_bo_reserved(bo)); in your
move_notify handler.
05/10 removed the loop and assumed no new fence could be attached after the
driver has
declared the bo dead.
However, at that point it may no longer hold a reservation to confirm this,
that's why
I moved the cleanup to be done in the release_list handler. It could still be
done in
ttm_bo_release, but we no longer have a reservation after we waited. Getting
a reservation can fail if the bo is imported for example.
While it would be true that in that case a new fence may be attached as well,
that
would be less harmful since that operation wouldn't involve this device, so the
ttm bo can still be removed in that case. When that time comes I should probably
fix up that WARN_ON(ret) in ttm_bo_cleanup_refs. :-)
I did add a WARN_ON(!atomic_read(&bo->kref.refcount)); to
ttm_bo_reserve and ttm_eu_reserve_buffers to be sure nothing is done on the
device
itself. If that is too paranoid, those WARN_ON's could be dropped. I prefer to
leave them
in for a kernel release or 2. But according to the rules that would be the only
time you
could attach a new fence and trigger the WARN_ON for now..
Hmm, I'd appreciate if you could group patches with functional changes that
depend on eachother togeteher,
and "this is done because ...", which makes it much easier to review, (and to
follow the commit history in case
something goes terribly wrong and we need to revert).
Meanwhile I'll take a look at the final ttm_bo.c and see if I can spot any
culprits.
In general, as long as a bo is on a LRU list, we must be able to attach fences
because of accelerated eviction.
I thought it was deliberately designed in such a way that it was kept on the
lru list,
but since it's also on the ddestroy list it won't start accelerated eviction,
since it branches into cleanup_refs early, and lru_lock still protects all the
list entries.
I used bad wording. I meant that unbinding might be accelerated, but currently
(quite inefficiently)
do synchronized unbinding, assuming that only the CPU can do that. When we
start to support
unsynchronized moves, we need to be able to attach fences at least at the last
move_notify(bo, NULL);
Would you need to wait in that case on fence_wait being completed before
calling move_notify?
If not, you would still only need to perform one wait, but you'd have to make
sure move_notify only gets
called by 1 thread before checking the fence pointer and performing a wait. At
that point you still hold the
lru_lock though, so it shouldn't be too hard to make something safe.
I think typically a driver that wants to implement asynchronous moves don't
want to wait before calling
move_notify, but may wait in move_notify or move. Typically (upcoming vmwgfx)
it would invalidate the buffer in move_notify(bo, NULL), attach a fence and
then use the normal delayed destroy to wait on that fence before destroying the
buffer.
Otherwise, since binds / unbinds are handled in the GPU command stream there's
never any need to wait for moves except when there's a CPU
access.
Well, nouveau actually needs fence_wait to finish first, since vm changes are
out of band.
But I guess it should be possible to attach it as work to the fence when it's
signaled, and I
may want to do something like that already for performance reasons in a
different place,
so I guess it doesn't matter.
Actions to be performed on fence signaling tend to be very cpu consuming, I
think due to the context switches involved.
We had to replace that in the old psb driver and batch things like TTM does
instead.
Also remember that TTM fences are not required to signal in finite time unless
fence_flush is called.
I think nouveau doesn't use fence irqs to signal its fences.
Is calling move_notify(bo, NULL) legal and a noop the second time?
I see no fundamental reason why it shouldn't be OK, although we might need to
patch drivers to cope with it.
That would save a flag in the bo to check if it's called already,
although I suppose we could always define a TTM_BO_PRIV_FLAG_* for it otherwise.
move_notify might end up being called with the lru_lock held, but that
shouldn't be a problem.
I don't think that's a good idea. Drivers sleeping in move_notify will need to
release the spinlock, and that means it's
better to release it before move_notify is called.
Is the only sleeping being done on fences? In that case we might wish to split
it up in 2 pieces for destruction,
the piece that runs immediately, and a piece to run after the new fence has
signaled (current behavior).
Nouveau needs the final move_notify unmap to be called after object is idle,
like it is now. It doesn't need
to attach a new fence.
In that case it might be best to worry about asynchronous stuff later?
We will eventually implement it on the new vmwgfx hardware revision, but
it's not ready yet.
/Thomas
~Maarten
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