On Mon, 21 May 2012, Rusty Russell wrote: > On Fri, 20 Apr 2012 16:18:04 +0200 (CEST), Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Fri, 20 Apr 2012, Srivatsa S. Bhat wrote: > > The whole notifier business needs a redesign as well, because we don't > > have a way to express proper dependencies, we add random notifier > > points and the teardown path is ass backwards. The whole thing wants > > to be a tree which can be walked in either direction and from any > > point. Right now we cut the trunk first and keep the single limb up > > with a helicopter and start dismantling it. > > But there are two ways to do it. One is to eliminate the need for > callbacks. The other is to make a full dependency-based callback What do you mean with fully eliminating the need for callbacks. Do you want to put the necessary bringup/shutdown function calls just in the core code so we get rid of the notifiers or do you have something different in mind ? > system. > > Let's try the first before the second. I implemented a full dep-based > system for initcalls once, and it was not as nice as I'd hoped. Yeah, a full dependency thing might be overkill. > > Flat notifiers are not working for this as they do not allow a tree > > structure and prevent us to do things in parallel. > > Not sure whether calling notifiers in parallel is going to be a big win: > they'll end up fighting over the cpu we're taking down. But I could be > wrong. I'm not going to aim for parallel in the first place. That was just an idea and if we chose the right implementation then parallelism can be added later. > > That really needs to be completely reworked. There is also a lot of > > stuff which wants to be moved into the starting/dying CPU > > context. Right now we kinda do that by trampling on the CPU with a > > high prio stomper thread, but that's really just a bandaid and steady > > cause of trouble. > > > > If you look at facilities which use kthreads, then there is lots other > > setup which does not need a notifier at all, as it can be done in the > > context of the thread when we have a way to start/park those threads > > at the right time in the up/down process. > > That's a very nice idea. Should be simpler for kthreads park/unpark > themselves, rather than having some notifier to kill them. Well, something needs to tell them to park/unpark, but what should move into the thread is the setup/teardown of context. > The original concept of stopping the machine for cpu hotplug and trying > not to effect any other kernel code has jumped the shark: I think we > need to look seriously at a complete rewrite where we don't use > stop_machine. Yep. Working on it. :) Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
