On Tue, Mar 11, 2014 at 11:34:21PM +0800, Ming Lei wrote: > >> In theory, it still might cause percpu_ida_alloc(TASK_RUNNING) failed, > >> looks it isn't a big deal for the case. > >> > >> But I am wondering why cpumask_set_cpu() isn't called with > >> holding lock inside percpu_ida_free()? Looks 'nr_free == 1' > >> shouldn't have happened frequently. > > > > Because bouncing on the lock is more expensive than occasionally putting > > a thread into sleep. > > I mean the below block can be put inside the previous lock: > > if (nr_free == 1) > cpumask_set_cpu() > > As I mentioned, 'nr_free == 1' doesn't happen frequently, so > it won't be big deal, will it?
No. The lock will be taken *each* time in your suggestion, which is bad. -- Regards, Alexander Gordeev [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
