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?
Cheers,
Jeff
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