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

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Message-ID: <20091005185024.GS1656@one.firstfloor.org>
Date:	Mon, 5 Oct 2009 20:50:24 +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 11:40:46AM -0700, Yinghai Lu wrote:
> Andi Kleen wrote:
> > 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.
> 
> I don't think so.

Let's put it like this: your BIOS does not describe the full system
topology which is a severe BIOS bug. Putting hacks into Linux
to work around that is not the right solution.

-Andi

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