On Thu, 29 Mar 2012 20:49:00 +0200 Daniel Vetter <daniel at ffwll.ch> wrote: > On Thu, Mar 29, 2012 at 11:43:12AM -0700, Ben Widawsky wrote: > > On Thu, 29 Mar 2012 20:24:11 +0200 > > Daniel Vetter <daniel at ffwll.ch> wrote: > > > > > On Sun, Mar 18, 2012 at 01:39:45PM -0700, Ben Widawsky wrote: > > > > Implement the context switch code as well as the interfaces to do the > > > > context switch. This patch also doesn't match 1:1 with the RFC patches. > > > > The main difference is that from Daniel's responses the last context > > > > object is now stored instead of the last context. This aids in allows us > > > > to free the context data structure, and context object independently. > > > > > > > > There is room for optimization: this code will pin the context object > > > > until the next context is active. The optimal way to do it is to > > > > actually pin the object, move it to the active list, do the context > > > > switch, and then unpin it. This allows the eviction code to actually > > > > evict the context object if needed. > > > > > > > > The context switch code is missing workarounds, they will be implemented > > > > in future patches. > > > > > > > > Signed-off-by: Ben Widawsky <ben at bwidawsk.net> > > > > > > Ok, I've looked at the use-sites of context_get and all this refcounting > > > and noticed that: > > > - we always hold dev->struct_mutex > > > - we always drop the acquired reference to the context structure in the > > > same function without dropping struct_mutex in between. > > > > > > So we don't seem to require any reference counting on these (and > > > additional locking on the idr). Additionally the idr locking seems to give > > > us a false sense of security because afaics the locking/refcounting would > > > be broken when we would _not_ hold struct_mutex. > > > > > > So can we just rip this out or do we need this (in which case it needs > > > some more work imo)? > > > -Daniel > > > > I think it can be ripped out. I was on the fence about this before > > submitting the patches and left it out of laziness; it doesn't hurt as > > there is no lock contention assuming your statement is true with no > > bugs in the code, and it follows the canonical use of idrs. > > > > Let me look it over some more to make sure after you finish reviewing > > the other stuff. The idea was supposed to be contexts can be created > > and looked up without struct mutex, but that isn't actually done in the > > code. > > Well, if you want to leave it I have to add some more review comments > about it - atm I think it would be buggy and racy without holding > struct_mutex ... > -Daniel As I said before, I'll either find a good use for it, or remove it. Context creation is the only currently viable case for it- but probably not worth the extra lock.
