Re: [RFC workqueue/driver-core PATCH 1/5] workqueue: Provide queue_work_near to queue work near a given NUMA node

Alexander Duyck
2018-10-02T18:28:22Z

On 10/2/2018 10:41 AM, Tejun Heo wrote:
> Hello,
>
> On Mon, Oct 01, 2018 at 02:54:39PM -0700, Alexander Duyck wrote:
>>> It might be better to leave queue_work_on() to be used for per-cpu
>>> workqueues and introduce queue_work_near() as you suggseted. I just
>>> don't want it to duplicate the node selection code in it. Would that
>>> work?
>>
>> So if I understand what you are saying correctly we default to
>> round-robin on a given node has no CPUs attached to it. I could
>> probably work with that if that is the default behavior instead of
>> adding much of the complexity I already have.
>
> Yeah, it's all in wq_select_unbound_cpu(). Right now, if the
> requested cpu isn't in wq_unbound_cpumask, it falls back to dumb
> round-robin. We can probably do better there and find the nearest
> node considering topology.

Well if we could get wq_select_unbound_cpu doing the right thing based
on node topology that would be most of my work solved right there.
Basically I could just pass WQ_CPU_UNBOUND with the correct node and it
would take care of getting to the right CPU.

>> The question I have then is what should I do about workqueues that
>> aren't WQ_UNBOUND if they attempt to use queue_work_near? In that
>
> Hmm... yeah, let's just use queue_work_on() for now. We can sort it
> out later and users could already do that anyway.
>
> Thanks.

So are you saying I should just return an error for now if somebody
tries to use something other than an unbound workqueue with
queue_work_near, and expect everyone else to just use queue_work_on for
the other workqueue types?

Thanks.

- Alex