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..
