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. ~Maarten _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
