linux-kernel - Re: [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the beginning of CPU

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Message-ID: <20160621194719.GU30154@twins.programming.kicks-ass.net>
Date:	Tue, 21 Jun 2016 21:47:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <htejun@...il.com>
Cc:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	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,
	kernel-team@...com
Subject: Re: [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the
 beginning of CPU_ONLINE

On Tue, Jun 21, 2016 at 03:43:56PM -0400, Tejun Heo wrote:
> On Tue, Jun 21, 2016 at 09:37:09PM +0200, Peter Zijlstra wrote:
> > Hurm.. So I've applied it, just to get this issue sorted, but I'm not
> > entirely sure I like it.
> > 
> > I think I prefer ego's version because that makes it harder to get stuff
> > to run on !active,online cpus. I think we really want to be careful what
> > gets to run during that state.
> 
> The original patch just did set_cpus_allowed one more time late enough
> so that the target kthread (in most cases) doesn't have to go through
> fallback rq selection afterwards.  I don't know what the long term
> solution is but CPU_ONLINE callbacks should be able to bind kthreads
> to the new CPU one way or the other.

Fair enough; clearly I need to stare harder. In any case, patch is on
its way to sched/urgent.