On 07.05.2012 23:28, Jerome Glisse wrote:
On Mon, May 7, 2012 at 4:38 PM, Christian König<deathsimple@xxxxxxxxxxx> wrote:
On 07.05.2012 20:52, Jerome Glisse wrote:
On Mon, May 7, 2012 at 1:59 PM, Jerome Glisse<j.glisse@xxxxxxxxx> wrote:
On 07.05.2012 17:23, Jerome Glisse wrote:
Your patch here can enter in infinite loop and never return holding
the lock. See below.
[SNIP]
+ } while (radeon_sa_bo_next_hole(sa_manager, fences));
Here you can infinite loop, in the case there is a bunch of hole in
the allocator but none of them allow to full fill the allocation.
radeon_sa_bo_next_hole will keep returning true looping over and over
on all the all. That's why i only restrict my patch to 2 hole skeeping
and then fails the allocation or try to wait. I believe sadly we need
an heuristic and 2 hole skeeping at most sounded like a good one.
Nope, that can't be an infinite loop, cause radeon_sa_bo_next_hole in
conjunction with radeon_sa_bo_try_free are eating up the opportunities
for
holes.
Look again, it probably will never loop more than RADEON_NUM_RINGS + 1,
with
the exception for allocating in a complete scattered buffer, and even
then
it will never loop more often than halve the number of current
allocations
(and that is really really unlikely).
Cheers,
Christian.
I looked again and yes it can loop infinitly, think of hole you can
never free ie radeon_sa_bo_try_free can't free anything. This
situation can happen if you have several thread allocating sa bo at
the same time while none of them are yet done with there sa_bo (ie
none have call sa_bo_free yet). I updated a v3 that track oldest and
fix all things you were pointing out above.
No that isn't a problem, radeon_sa_bo_next_hole takes the firsts entries of
the flist, so it only considers holes that have a signaled fence and so can
be freed.
Having multiple threads allocate objects that can't be freed yet will just
result in empty flists, and so radeon_sa_bo_next_hole will return false,
resulting in calling radeon_fence_wait_any with an empty fence list, which
in turn will result in an ENOENT and abortion of allocation (ok maybe we
should catch that and return -ENOMEM instead).
So even the corner cases should now be handled fine.
No, there is still infinite loop possible with gpu lockup, i am
against the while (next_hole) using for on 2 iteration looks a lot
better and it avoids sa allocator possibly looping too much (because
it can loop a lot more than RADEON_NUM_RINGS, the maximum number of
loop is sa_manager->size/4).
I'm still pretty sure that there isn't the possibility for an infinite
loop, so please explain further where exactly the problem is.
radeon_sa_bo_next_hole will return true as long as it can find AND
remove an allocation with an already signaled fence, and since nobody
else can add allocations while we are in the loop we sooner or later run
out of allocations and so the loop ends.
Also what the loop does is just cleaning up all the already signaled
allocations, and it doesn't matter if there is one allocation or a
million, we need to clean them up anyway. So aborting the loop and
trying to wait for anything to be signaled makes no sense at all, and
aborting the whole allocation at this point makes even less sense, cause
that only delays the work that needs to be done anyway (freeing the
allocations) to a later call to radeon_sa_bo_new.
What could make sense is limiting how often we are waiting for some
fences, since while waiting we release the lock and then other processes
can jump in and grab what we wanted to have by waiting for something to
happen.
Cheers,
Christian.
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel
