Replaying what Oleg wrote: (add lkml)
> Replaying what Tejun wrote: > Replacing get_online_cpus() w/ percpu_rwsem is great but this thread > is about replacing preempt_disable with something finer grained and > less heavy on the writer side If only I understood why preempt_disable() is bad ;-) OK, I guess "less heavy on the writer side" is the hint, and in the previous email you mentioned that "stop_machine() itself is extremely heavy". Looks like, you are going to remove stop_machine() from cpu_down ??? > The problem seems that we don't have percpu_rwlock yet. It shouldn't > be too difficult to implement, right? > Oh, I am not sure... unless you simply copy-and-paste the lglock code and replace spinlock_t with rwlock_t. We probably want something more efficient, but I bet we can't avoid the barriers on the read side. And somehow we should avoid the livelocks. Say, we can't simply add the per_cpu_reader_counter, _read_lock should spin if the writer is active. But at the same time _read_lock should be recursive. Tejun, could you please send me mbox with this thread offlist? [That should now be unnecessary, since the discussion can continue on-list on this thread]. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
