On Fri, 2011-05-27 at 12:36 +0200, Ingo Molnar wrote: > * Sasha Levin <levinsasha928@xxxxxxxxx> wrote: > > > I see that in liburcu there is an implementation of a rcu linked > > list but no implementation of a rb-tree. > > Another approach would be, until the RCU interactions are sorted out, > to implement a 'big reader lock' thing that is completely lockless on > the read side (!). > > It works well if the write side is expensive, but very rare: which is > certainly the case for these ioport registration data structures used > in the mmio event demux fast path! > > The write_lock() side signals all worker threads to finish whatever > they are doing now and to wait for the write_unlock(). Then the > modification can be done and the worker threads can be resumed. > > This can be updated to RCU later on without much trouble. > > The advantage is that this could be implemented with the existing > thread-pool primitives straight away i think, we'd need five > primitives: > > bread_lock(); > bread_unlock(); > bwrite_lock(); > bwrite_lock(); > > brlock_init(); > > and a data type: > > struct brlock; > > bread_lock()/bread_unlock() is basically just a compiler barrier. > bwrite_lock() stops all (other) worker threads. > bwrite_unlock() resumes them. > > That's all - should be 50 lines of code, unless i'm missing something > :-) > > Thanks, > > Ingo Isn't there something similar to this in the kernel? I prefer not implementing a new lock type at the moment mostly because we're not tackling a bug or an immediate problem, we don't really need locking at the moment (we add all devices at init and don't support hotplug yet). So I'd rather not write code just to solve it faster but have it thrown away later. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
