linux-kernel - Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a node with 1 online CPU

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Message-ID: <1466079084.19127.2.camel@ellerman.id.au>
Date:	Thu, 16 Jun 2016 22:11:24 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Tejun Heo <htejun@...il.com>, Peter Zijlstra <peterz@...radead.org>
Cc:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a
 node with 1 online CPU

On Wed, 2016-06-15 at 12:01 -0400, Tejun Heo wrote:
> On Wed, Jun 15, 2016 at 03:14:15PM +0200, Peter Zijlstra wrote:
> > On Wed, Jun 15, 2016 at 06:20:33PM +0530, Gautham R Shenoy wrote:
> > > We will no longer have the optimization in
> > > restore_unbound_workers_cpumask() but I suppose we don't lose much by
> > > resetting the affinity every time a CPU in the pool->attr->cpumask
> > > comes online.
> > 
> > Right; optimizing hotplug really isn't worth it. The code needs to be
> > simple and robust (ha! funny).
> 
> The only case it might matter is CPU hotplug being used aggressively
> for power saving.  No idea how popular that is now tho.
> set_cpus_allowed isn't that expensive and phones don't tend to have
> massive number of kworkers, so hopefully it won't show up.
> 
> > In any case, Tejun, does this work for you?
> 
> I'm not sure about the reordering part but for setting affinity on
> each onlining, no objection.  If it ever shows up as performance /
> power regression, we can revisit it later.

Peterz do you want to send a SOB'ed patch, or can we take what you posted and
add your SOB?

And Tejun are you happy to merge this for rc4?

cheers