On 2012-12-04 21:23, Jeff Moyer wrote:
> 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.
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.
--
Jens Axboe
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