Hello, On Wed, Jul 25, 2012 at 05:25:13PM +0530, Srivatsa S. Bhat wrote: > During CPU hotplug, we want to create the following effect: > * During CPU online, the CPU incrementally grows the number of services > it offers. > * During CPU offline, the services are incrementally retired, in the > reverse order of their growth during CPU online. > > To achieve the above, invoke the registered CPU hotplug notifiers in the > reverse order during CPU offline, with respect to the order in which they > were invoked during CPU online. > > This approach helps in making the hotplug path a lot more logically > coherent: Services are started in a well-known order, perhaps with > dependencies > between them, while bringing up a CPU. While offlining the CPU, we honor > many of the dependencies automatically by just backtracking the way we came; > that is, by invoking the notifiers in the reverse order. Thus, this model of > reverse notifier invocation helps us in avoiding the need for excessively > messing with the notifier priorities while trying to get the ordering right. > > Notes: > 1. The workqueue code becomes simpler, since it now needs just a single CPU > hotplug callback. > 2. The scheduler's sched_cpu_[in]active() callbacks can also be merged into > a single callback. > 3. On similar lines, the cpusets' cpuset_cpu_[in]active() callbacks can also > be merged. > > Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
For workqueue part, Acked-by: Tejun Heo <t...@kernel.org> Now that we can reverse-walk notifier chain, it probably is a good idea to make it a bit smarter and call CANCELs in reverse order of PREPAREs too. Thanks. -- tejun -- 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/
