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

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Date:   Tue, 2 Oct 2018 11:23:26 -0700
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     linux-nvdimm@...ts.01.org, gregkh@...uxfoundation.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, len.brown@...el.com,
        dave.jiang@...el.com, rafael@...nel.org, vishal.l.verma@...el.com,
        jiangshanlai@...il.com, pavel@....cz, zwisler@...nel.org,
        dan.j.williams@...el.com
Subject: Re: [RFC workqueue/driver-core PATCH 1/5] workqueue: Provide
 queue_work_near to queue work near a given NUMA node

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