linux-kernel - Re: [RFC][PATCH 14/26] sched, numa: Numa balancer

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Date:	Sat, 14 Jul 2012 12:20:46 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Don Morris <don.morris@...com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 14/26] sched, numa: Numa balancer

On 07/13/2012 10:45 AM, Don Morris wrote:

>> IIRC the test consisted of a 16GB NUMA system with two 8GB nodes.
>> It was running 3 KVM guests, two guests of 3GB memory each, and
>> one guest of 6GB each.
>
> How many cpus per guest (host threads) and how many physical/logical
> cpus per node on the host? Any comparisons with a situation where
> the memory would fit within nodes but the scheduling load would
> be too high?

IIRC this particular test was constructed to have guests
A and B fit in one NUMA node, with guest C in the other
NUMA node.

With schednuma, guest A ended up on one NUMA node, guest
B on the other, and guest C was spread between both nodes.

Only migrating when there is plenty of free space available
means you can end up not doing the right thing when running
a few large workloads on the system.

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