On 2012-12-04 23:26, Jeff Moyer wrote: > Jens Axboe <jaxboe@xxxxxxxxxxxx> writes: > >>>>> @@ -437,6 +488,14 @@ static int bdi_forker_thread(void *ptr) >>>>> spin_lock_bh(&bdi->wb_lock); >>>>> bdi->wb.task = task; >>>>> spin_unlock_bh(&bdi->wb_lock); >>>>> + mutex_lock(&bdi->flusher_cpumask_mutex); >>>>> + ret = set_cpus_allowed_ptr(task, >>>>> + bdi->flusher_cpumask); >>>>> + mutex_unlock(&bdi->flusher_cpumask_mutex); >>>> >>>> It'd be very useful if we had a kthread_create_cpu_on_cpumask() instead >>>> of a _node() variant, since the latter could easily be implemented on >>>> top of the former. But not really a show stopper for the patch... >>> >>> Hmm, if it isn't too scary, I might give this a try. >> >> Should not be, pretty much just removing the node part of the create >> struct passed in and making it a cpumask. And for the on_node() case, >> cpumask_of_ndoe() will do the trick. > > I think it's a bit more involved than that. If you look at > kthread_create_on_node, the node portion only applies to where the > memory comes from, it says nothing of scheduling. To whit: > > /* > * root may have changed our (kthreadd's) priority or CPU mask. > * The kernel thread should not inherit these properties. > */ > sched_setscheduler_nocheck(create.result, SCHED_NORMAL, ¶m); > set_cpus_allowed_ptr(create.result, cpu_all_mask); > > So, if I were to make the change you suggested, I would be modifying the > existing behaviour. The way things stand, I think > kthread_create_on_node violates the principal of least surprise. ;-) I > would prefer a variant that affected scheduling behaviour as well as > memory placement. Tejun, Peter, Ingo, what are your opinions? Huh you are right, I completely missed that set_cpus_allowed_ptr() uses cpu_all_mask and not mask_of_node(node). Doesn't make a lot of sense to me... And yes, in any case, it definitely is a bad API, not very logical. -- Jens Axboe -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>