linux-kernel - Re: [PATCH] x86: use near online node instead of round bin for numa

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Date:	Mon, 5 Oct 2009 20:35:39 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: use near online node instead of round bin for numa

On Mon, Oct 05, 2009 at 11:09:59AM -0700, Yinghai Lu wrote:
> Andi Kleen wrote:
> > Yinghai Lu <yinghai@...nel.org> writes:
> > 
> >> cpu to node mapping is set in following sequence:
> >> 1. numa_init_array: set up roundbin from cpu to online node
> >> 2. init_cpu_to_node: set that according to apicid_to_node[] according to srat
> >> 		  only handle that node is online, and leave other cpu on node
> >> 		  without ram (aka not online) to still round-bin
> >> 3. later srat_detect_node for intel/amd, will use first_online node or near by
> >>    node.
> >>
> >> problem is that setup_per_cpu_areas() is called between  2 and 3. the per_cpu
> >> for cpu on node with ram is on different node. and could put that on node with
> >> two hops away.
> >>
> >> so try add find_near_online_node() and call int init_cpu_to_node()
> > 
> > This fallback case should not really happen anyways, unless the BIOS is buggy
> > (in this case it might better to completely reject the SRAT because
> > more might be wrong).
> SRAT is right, and some node has no ram installed.

In this case there should be still a PXM to define the CPU locality -- your BIOS is broken.
Please fix it there.

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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