>>> On Wed, Jun 18, 2008 at 8:42 AM, in message <200806182242.49245.nickpiggin@xxxxxxxxxxxx>, Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote: > On Wednesday 18 June 2008 22:25, Gregory Haskins wrote: >> >>> On Wed, Jun 18, 2008 at 8:16 AM, in message > >> > Yeah - migrate_disable() has been proposed several times. The reason I >> > don't like it is that is creates scheduling artefacts like latencies by >> > not being able to load-balance (and thereby complicates all that, and >> > you know we don't need more complication there). >> >> True, and good point. But this concept would certainly be useful to avoid >> the heavyweight (w.r.t. latency) preempt-disable() in quite a few different >> areas, so if we can make it work with reasonable visibility, it might be >> nice to have. > > It just seems like pretty worthless bloat to me. > > There are _some_ cases where it can be used, but nobody has been > able to come up with compelling uses really. Well, I have some ongoing R&D which (I believe) *would* make compelling use of a migration-disable feature. But to date it is not ready to see the light of day. As far as existing uses, I think I mostly agree with you. The one argument to the contrary would be to clean up the handful of places that implement an ad-hoc migration-disable by messing with cpus_allowed in a similar manner. But perhaps those could be solved with a preempt-disable() as well. >I don't think this > case is helped very much either because the logic in there using > preempt-disable is fine, isn't it? You are probably right. In my own defense, I was just responding to the question about manipulating the cpus_allowed. If you are going to do that you are better off with my patch (IMO). Changing cpus_allowed to prevent migration is racy, among other things. Whether this tsc code is optimal with migration disabled or preemption-disabled is a separate matter which I did not address. > > Except that it should also have a cond_resched in it. Seems like > an ideal place to put cond_resched because it is not a fastpath. Seems reasonable to me. Thanks Nick. -Greg -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
