Jens Axboe <jaxboe@xxxxxxxxxxxx> writes:
> On 2012-12-03 19:53, Jeff Moyer wrote:
>> Hi,
>>
>> In realtime environments, it may be desirable to keep the per-bdi
>> flusher threads from running on certain cpus. This patch adds a
>> cpu_list file to /sys/class/bdi/* to enable this. The default is to tie
>> the flusher threads to the same numa node as the backing device (though
>> I could be convinced to make it a mask of all cpus to avoid a change in
>> behaviour).
>
> Looks sane, and I think defaulting to the home node is a sane default.
> One comment:
>
>> + ret = cpulist_parse(buf, newmask);
>> + if (!ret) {
>> + spin_lock(&bdi->wb_lock);
>> + task = wb->task;
>> + if (task)
>> + get_task_struct(task);
>> + spin_unlock(&bdi->wb_lock);
>
> bdi->wb_lock needs to be bh safe. The above should have caused lockdep
> warnings for you.
No lockdep complaints. I'll double check that's enabled (but I usually
have it enabled...).
>> @@ -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.
Thanks!
Jeff
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