On Fri, Aug 10, 2018 at 01:17:14PM +1000, NeilBrown wrote: > On Thu, Aug 09 2018, J. Bruce Fields wrote: > > > On Fri, Aug 10, 2018 at 11:50:58AM +1000, NeilBrown wrote: > >> You're good at this game! > > > > Everybody's got to have a hobby, mine is pathological posix locking > > cases.... > > > >> So, because a locker with the same "owner" gets a free pass, you can > >> *never* say that any lock which conflicts with A also conflicts with B, > >> as a lock with the same owner as B will never conflict with B, even > >> though it conflicts with A. > >> > >> I think there is still value in having the tree, but when a waiter is > >> attached under a new blocker, we need to walk the whole tree beneath the > >> waiter and detach/wake anything that is not blocked by the new blocker. > > > > If you're walking the whole tree every time then it might as well be a > > flat list, I think? > > The advantage of a tree is that it keeps over-lapping locks closer > together. > For it to make a difference you would need a load where lots of threads > were locking several different small ranges, and other threads were > locking large ranges that cover all the small ranges. OK, I'm not sure I understand, but I'll give another look at the next version.... > I doubt this is common, but it doesn't seem as strange as other things > I've seen in the wild. > The other advantage, of course, is that I've already written the code, > and I like it. > > Maybe I'll do a simple-list version, then a patch to convert that to the > clever-tree version, and we can then have something concrete to assess. That might help, thanks. --b.
