* Matt Mackall ([EMAIL PROTECTED]) wrote: > On Wed, Jul 11, 2007 at 10:02:23AM +1000, Nick Piggin wrote: > > >I like this patch a lot. Even if we don't add the underlying mechanism > > >right now, adding migration_disable as an alias for preempt_disable > > >will much better document quite a number of the users. > > > > I'd have no problem with that, and it might make it easier in future to > > justify a more complex scheme. > > What do you think, Mathieu? >
That's an excellent idea. It should probably come with some documentation explaining what difference should be expected between preempt_disable and migrate_disable in the future so that people can choose the right alternative for their code. > Also, small nit: it ought to be migrate_disable to match the form of > preempt_disable. Yes, that's fine with me. :) I though a little more about this whole concept of migrate_disable, and I think it could be brought further. One of the main problems with per cpu variables is that this concept cannot be ported to this grey place called "user-space" because preemption cannot be disabled. The equivalent (kind of) is currently per thread variables, but it can consume a lot of space if many threads are running. However, it could be possible, if we implement a vsyscall based migration preemption counter accessible with read/write access from user-space, to tie a thread to a CPU during a user-space critical path. If we combine this with local atomic operations done in user-space, we could have highly scalable access to per cpu data structures reentrant with respect to signal handlers. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
