On Thu, May 02, 2024 at 03:33:50PM +0100, Tvrtko Ursulin wrote: > > Hi all, > > Continuing after the brief IRC discussion yesterday regarding work queues > being prone to deadlocks or not, I had a browse around the code base and > ended up a bit confused. > > When drm_sched_init documents and allocates an *ordered* wq, if no custom > one was provided, could someone remind me was the ordered property > fundamental for something to work correctly? Like run_job vs free_job > ordering? > Before the work queue (kthread design), run_job & free_job were ordered. It was decided to not break this existing behavior. > I ask because it appears different drivers to different things and at the > moment it looks we have all possible combos or ordered/unordered, bound and > unbound, shared or not shared with the timeout wq, or even unbound for the > timeout wq. > > The drivers worth looking at in this respect are probably nouveau, panthor, > pvr and xe. > > Nouveau also talks about a depency betwen run_job and free_job and goes to > create two unordered wqs. > > Then xe looks a bit funky with the workaround/hack for lockep where it > creates 512 work queues and hands them over to user queues in round-robin > fashion. (Instead of default 1:1.) Which I suspect is a problem which should > be applicable for any 1:1 driver given a thorough enough test suite. > I think lockdep ran out of chains or something when executing some wild IGT with 1:1. Yes, any driver with a wild enough test would likely hit this lockdep splat too. Using a pool probably is not bad idea either. > So anyway.. ordered vs unordered - drm sched dictated or at driver's choice? > Default ordered, driver can override with unordered. Matt > Regards, > > Tvrtko
