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

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Message-ID: <20160621194356.GU3262@mtj.duckdns.org>
Date:	Tue, 21 Jun 2016 15:43:56 -0400
From:	Tejun Heo <htejun@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 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.

Thanks.

-- 
tejun