linux-kernel - Re: [PATCH 09/40] autonuma: introduce kthread_bind

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Date:	Thu, 5 Jul 2012 22:33:35 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 09/40] autonuma: introduce kthread_bind_node()

On 07/05/2012 05:09 PM, Johannes Weiner wrote:
> In the very first review iteration of AutoNUMA, Peter argued that the
> scheduler people want to use this flag in other places where they rely
> on this thing meaning a single cpu, not a group of them (check out the
> cpumask test in debug_smp_processor_id() in lib/smp_processor_id.c).
> 
> He also argued that preventing root from rebinding the numa daemons is
> not critical to this feature at all.  And I have to agree.

Despite not being a scheduler expert, I'll have to side with that as
well. The thing I have in mind is: We have people whose usecase depend
on completely isolating cpus, with nothing but a specialized task
running on it. For those people, even the hard binding between cpu0 and
the timer interrupt is a big problem.

If you force a per-node binding of a kthread, you are basically saying
that those people are unable to isolate a node. Or else, that they have
to choose between that, and AutoNUMA. Both are suboptimal choices, to
say the least.

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