linux-kernel - Re: [PATCH] Fake NUMA emulation for PowerPC

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Message-ID: <4759C89B.9000709@linux.vnet.ibm.com>
Date:	Sat, 08 Dec 2007 03:56:35 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Nathan Lynch <ntl@...ox.com>
CC:	linuxppc-dev@...abs.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fake NUMA emulation for PowerPC

Nathan Lynch wrote:
> Hi Balbir-
> 
> Balbir Singh wrote:
>>
>> Here's a dumb simple implementation of fake NUMA nodes for PowerPC. Fake
>> NUMA nodes can be specified using the following command line option
>>
>> numa=fake=<node range>
>>
>> node range is of the format <range1>,<range2>,...<rangeN>
>>
>> Each of the rangeX parameters is passed using memparse(). I find the patch
>> useful for fake NUMA emulation on my simple PowerPC machine. I've tested it
>> on a non-numa box with the following arguments
>>
>> numa=fake=1G
>> numa=fake=1G,2G
>> name=fake=1G,512M,2G
>> numa=fake=1500M,2800M mem=3500M
>> numa=fake=1G mem=512M
>> numa=fake=1G mem=1G
> 
> So this doesn't appear to allow one to assign cpus to fake nodes?  Do
> all cpus just get assigned to node 0 with numa=fake?
> 

Yes, they all appear on node 0. We could have tweaks to distribute CPU's
as well.

> A different approach that occurs to me is to use kexec with a doctored
> device tree (i.e. with the ibm,associativity properties modified to
> reflect your desired topology).  Perhaps a little bit obscure, but it
> seems more flexible.
> 

That would be interesting, but it always means that we need to run
kexec, which might involve two boots.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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