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

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Date:	Mon, 05 Oct 2009 11:09:59 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	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

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.
> 
> Do you have a system where this is needed?

sure.

YH
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