On 11/28/2012 01:15 PM, Maarten Lankhorst wrote: > Op 28-11-12 12:54, Thomas Hellstrom schreef: >> On 11/28/2012 12:25 PM, Maarten Lankhorst wrote: >>> By removing the unlocking of lru and retaking it immediately, a race is >>> removed where the bo is taken off the swap list or the lru list between >>> the unlock and relock. As such the cleanup_refs code can be simplified, >>> it will attempt to call ttm_bo_wait non-blockingly, and if it fails >>> it will drop the locks and perform a blocking wait, or return an error >>> if no_wait_gpu was set. >>> >>> The need for looping is also eliminated, since swapout and evict_mem_first >>> will always follow the destruction path, so no new fence is allowed >>> to be attached. As far as I can see this may already have been the case, >>> but the unlocking / relocking required a complicated loop to deal with >>> re-reservation. >>> >>> The downside is that ttm_bo_cleanup_memtype_use is no longer called with >>> reservation held, so drivers must be aware that move_notify with a null >>> parameter doesn't require a reservation. >> Why can't we unreserve *after* ttm_bo_cleanup_memtype_use? That's not >> immediately clear from this patch. > Because we would hold the reservation while waiting and with the object still > on swap and lru lists still, that would defeat the whole purpose of keeping > the object on multiple lists, plus break current code that assumes bo's on the > those lists can always be reserved. > > the if (ret && !no_wait_gpu) path has to drop the reservation and lru lock, > and > isn't guaranteed to be able to retake it. Maybe it could be guaranteed now, > but > I'm sure that would not be the case if the reservations were shared across > devices. The evict path removes the BO from the LRU lists, drops the LRU lock but hangs on to the reservation, and in case the wait goes wrong, re-adds the bo to the LRU lists and returns an error.
Isn't it possible to do the same in the !no_wait_gpu case? /Thomas
