On Thu, 2014-02-13 at 10:56 +0000, Srivatsa S. Bhat wrote: > On 02/12/2014 11:48 AM, Srivatsa S. Bhat wrote: : > >>> For example, something like the code snippet shown below looks pretty > >>> neat to me: > >>> > >>> cpu_notifier_register_begin(); > >>> > >>> for_each_online_cpu(cpu) > >>> init_cpu(cpu); > >>> > >>> register_cpu_notifier(&foobar_cpu_notifier); > >>> > >>> cpu_notifier_register_done(); > >>> > >>> What do you think? > >> > >> I agree that it is cleaner for the callers as long as people understand > >> how to use them. Can you document them properly so that they know when > >> they need to use them instead of the familiar get/put_online_cpus()? > >> > > > > Sure.. I had updated the documentation with the semantics introduced in > > this patchset, in patch 2: > > > > http://thread.gmane.org/gmane.linux.kernel/1641638/focus=1641695 > > > > Similarly I'll keep the docs updated with these new APIs in v2 as well. > > > > For now, however, let us not add the new rw-semaphore to the CPU hotplug > core yet. Its very unlikely that we'll see any performance issue immediately, > due to serialized initialization of cpu hotplug notifiers, since early boot > is mostly sequential anyway. > > Some time in the future, if we start hitting bottlenecks in the cpu hotplug > notifier registration phase (perhaps when we implement parallel CPU boot-up > infrastructure), then we can directly use the rw-semaphore solution, since > we have already worked it out. Besides, like Gautham said, we might want > to be more careful and have a very good justification before adding more > locks to the CPU hotplug core code. So we'll add the new rw-sempahore if > and when it becomes necessary. > > I'll post the v2 with the earlier design itself, by adding the new symbols > cpu_notifier_register_begin/done() (to enhance the readability) and map > them to cpu_maps_update_begin/done().
Sounds reasonable to me. I was also concerned about exporting and overloading cpu_maps_update_begin/done() for a different purpose (their purpose is to update cpu_maps). So, I think adding the new interfaces is good when we cannot use get/set_online_cpus() for this. Thanks, -Toshi -- 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/
