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

[Alexander Duyck]

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