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On Tue, Jan 20, 2004 at 06:45:37PM +1100, Nick Piggin wrote: > >I guess a hotplug script MAY fail. I don't think it's a good idea to make > >your CPU hotplug script fail. May and Misght are different. It's up to > >the > >implementor whether the script can get into a failure condition. > > > > Sorry bad wording. The script may fail to be executed. Under what conditions? Not arbitrary entropy, surely. If a hotplug script is present and does not blow up, it should be safe to assume it will be run upon an event being delivered. If not, we have a WAY bigger problem :) > >What if <which> process needs guaranteed scheduling latency? Do we really > >_guarantee_ scheduling latency *anywhere*? > > We do guarantee that a realtime task won't be blocked waiting for > a hotplug script to fault in and start it up again (which may not > happen). Not sure how important this issue is. We have a conflict of priority here. If an RT task is affined to CPU A and CPU A gets yanked out, what do we do? Obviously the RT task can't keep running as it was. It was affined to A. Maybe for a good reason. I see we have a few choices here: * re-affine it automatically, thereby silently undoing the explicit affinity. * violate it's RT scheduling by not running it until it has been re-affined or CPU A returns to the pool/ Sending it a SIGPWR means you have to run it on a different CPU that it was affined to, which is already a violation. Basically, RT tasks + CPU affinity + hotplug CPUs do not play nicely together. I don't see much that can be done to solve that. With the procstate stuff I did, and with planned CPU unplugs we *do* have time before the CPU really goes offline in which to act. With unplanned CPU offlining, we don't. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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