Message-ID: <4759C6C5.2000100@linux.vnet.ibm.com>
Date: Sat, 08 Dec 2007 03:48:45 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
Organization: IBM
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To: Kumar Gala <galak@kernel.crashing.org>
CC: Olof Johansson <olof@lixom.net>, linuxppc-dev@ozlabs.org,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Fake NUMA emulation for PowerPC
References: <20071207211425.10223.91240.sendpatchset@balbir-laptop> <20071207212817.GA391@lixom.net> <4759BCA2.1020809@linux.vnet.ibm.com> <975B5B2B-C1F3-4021-9AE2-8873FFE1BDEC@kernel.crashing.org> <4759C548.6030304@linux.vnet.ibm.com> <9AEDD952-7F20-471C-9A82-B6F3254BC869@kernel.crashing.org>
In-Reply-To: <9AEDD952-7F20-471C-9A82-B6F3254BC869@kernel.crashing.org>
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Kumar Gala wrote:
> 
> On Dec 7, 2007, at 4:12 PM, Balbir Singh wrote:
> 
>> Kumar Gala wrote:
>>>
>>> On Dec 7, 2007, at 3:35 PM, Balbir Singh wrote:
>>>
>>>> Olof Johansson wrote:
>>>>> Hi,
>>>>>
>>>>> On Sat, Dec 08, 2007 at 02:44:25AM +0530, Balbir Singh wrote:
>>>>>
>>>>>> Comments are as always welcome!
>>>>>
>>>>> Care to explain what this is useful for? (Not saying it's a stupid
>>>>> idea,
>>>>> just wondering what the reason for doing it is).
>>>>>
>>>>
>>>> In my case, I use it to test parts of my memory controller patches
>>>> on an
>>>> emulated NUMA machine. I plan to use it to test out page migration
>>>> across nodes.
>>>
>>> Can you explain that further.  I'm still not clear on why this is
>>> useful.
>>>
>>> - k
>>
>> Sure. In my case I need to emulate NUMA nodes to do some NUMA specific
>> testing. The memory controller I've written has some interesting data
>> structures like per node, per zone LRU lists. To be able to test those
>> features on a non-numa box is a problem, since we get just the default
>> node.
> 
> Maybe I'm missing something, what do you mean by memory controller
> you've written?  (I'm use to the term 'memory controller' meaning the
> actual RAM control).
> 

Ah! that explains the disconnect. If you look at the latest -mm tree. We
have a memory controller under control groups, we use it to control how
much memory a group of process can access at a time.

>> To be able to test the memory controller under NUMA, I use fake NUMA
>> nodes. x86-64 has a similar feature, the code I have here is the
>> simplest I could come up with for PowerPC.
>>
>> I just thought of another very interesting use case, it can be used to
>> split up the zone's lru lock which is highly contended.
> 
> - k


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