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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Message-ID: <20181002174116.GG270328@devbig004.ftw2.facebook.com>
Date:   Tue, 2 Oct 2018 10:41:16 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
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

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.

> 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.

-- 
tejun