Am 21.02.2018 um 11:54 schrieb Maarten Lankhorst: > Op 21-02-18 om 00:56 schreef Daniel Vetter: >> On Tue, Feb 20, 2018 at 04:21:58PM +0100, Peter Zijlstra wrote: >>> On Tue, Feb 20, 2018 at 04:05:49PM +0100, Christian König wrote: >>>> Am 20.02.2018 um 15:54 schrieb Peter Zijlstra: >>>>> On Tue, Feb 20, 2018 at 03:34:07PM +0100, Christian König wrote: >>>>>>> OK, but neither case would in fact need the !ctx case right? That's just >>>>>>> there for completeness sake? >>>>>> Unfortunately not. TTM uses trylock to lock BOs which are about to be >>>>>> evicted to make room for all the BOs locked with a ctx. >>>>>> >>>>>> I need to be able to distinct between the BOs which are trylocked and those >>>>>> which are locked with a ctx. >>>>>> >>>>>> Writing this I actually noticed the current version is buggy, cause even >>>>>> when we check the mutex owner we still need to make sure that the ctx in the >>>>>> lock is NULL. >>>>> Hurm... I can't remember why trylocks behave like that, and it seems >>>>> rather unfortunate / inconsistent. >>>> Actually for me that is rather fortunate, cause I need to distinct between >>>> the locks acquired through trylock and lock. >>> I suppose that would always be possible using: >>> ww_mutex_trylock(.ctx=NULL), and it could be that there simply weren't >>> any immediate uses for a !NULL trylock and it was thus not implemented. >>> >>> But that is all very long ago.. >> I think we simple never had a use-case for interleaving ww_mutex_lock(ctx) >> and ww_mutex_trylock(ctx). Nesting multiple trylocks in ctx-locks happens >> plenty, but not further: >> >> The common use-case for that is locking a bunch of buffers you need (for >> command submission or whatever), and then trylocking other buffers to make >> space for the buffers you need to move into VRAM. I guess if only >> trylocking buffers doesn't succeed in freeing up enough VRAM then we could >> go into blocking ww_mutex_locks which need the ctx (and which would need >> all the trylock-acquired buffers to be annotated with the ctx too). TTM >> currently tries to be far enough away from that corner case (using a >> defensive "never use more than 50% of all memory for gfx" approach) that >> it doesn't seem to need that. >> >> Once we get there it should indeed be simply to add a ctx parameter to >> ww_mutex_trylock to fix this case. The TTM side rework is definitely going >> to be the much bigger issue here ... >> -Daniel > Yes, I think fixing trylock to take a ctx parameter would be a better fix than ww_mutex_is_owned_by.. Yeah, but as I noted now multiple times that won't work. See I need to distinct between the BOs acquired with and without a context. Otherwise the whole approach doesn't make much sense. Christian.
