On Wed, 25 Jul 2012, Srivatsa S. Bhat wrote: > On 07/25/2012 08:27 PM, Alan Stern wrote: > One of the other ideas to improve the hotplug notifier stuff that came up > during some > of the discussions was to implement explicit dependency tracking between the > notifiers > and perhaps get rid of the priority numbers that are currently being used to > provide > some sort of ordering between the callbacks. Links to some of the related > discussions > are provided below.
The current code which brings up/down a CPU (mostly architecture specific) code is comnpletely asymetric. We really want a fully symetric state machine here, which also gives us the proper invocation points for the other subsystems callbacks. While I thought about having a full dependency tracking system, I'm quite convinced by now, that hotplug is a rather linear sequence which does not provide much room for paralell setup/teardown. At least we should start with a simple linear chain. The problem with the current notifiers is, that we only have ordering for a few specific callbacks, but we don't have the faintest idea in which order all other random stuff is brought up and torn down. So I started experimenting with the following: struct hotplug_event { int (*bring_up)(unsigned int cpu); int (*tear_down)(unsigned int cpu); }; enum hotplug_events { CPU_HOTPLUG_START, CPU_HOTPLUG_CREATE_THREADS, CPU_HOTPLUG_INIT_TIMERS, ... CPU_HOTPLUG_KICK_CPU, ... CPU_HOTPLUG_START_THREADS, ... CPU_HOTPLUG_SET_ONLINE, ... CPU_HOTPLUG_MAX_EVENTS, }; Now I have two arrays: struct hotplug_event hotplug_events_bp[CPU_HOTPLUG_MAX_EVENTS]; struct hotplug_event hotplug_events_ap[CPU_HOTPLUG_MAX_EVENTS]; The _bp one is the list of events which are executed on the active cpu and the _ap ones are those executed on the hotplugged cpu. The core code advances the events in sync steps, so both BP and AP can issue a stop on the process and cause a rollback. Most of the callbacks can be added to the arrays at compile time, just the stuff which is in modules requires an register/unregister interface. Though in any case the enum gives us a very explicit ordering of setup/teardown, so rollback or partial online/offline should be simple to achieve. The only drawback is that it will prevent out of tree modules to use the hotplug infrastructure, but I really couldn't care less. Thoughts? tglx -- 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/