Re: [PATCH 00/07][RFC] i386: NUMA emulation

["Martin J. Bligh" <mbligh@mbligh.org>]

--David Lang <david.lang@digitalinsight.com> wrote (on Monday, October 03, 2005 08:32:47 -0700):

> On Mon, 3 Oct 2005, Martin J. Bligh wrote:
> 
>> --David Lang <david.lang@digitalinsight.com> wrote (on Monday, October 03, 2005 08:13:09 -0700):
>> 
>>> On Mon, 3 Oct 2005, Martin J. Bligh wrote:
>>> 
>>>> --David Lang <david.lang@digitalinsight.com> wrote (on Monday, October 03, 2005 08:03:44 -0700):
>>>> 
>>>>> On Mon, 3 Oct 2005, Martin J. Bligh wrote:
>>>>> 
>>>>>> But that's not the same at all! ;-) PAE memory is the same speed as
>>>>>> the other stuff. You just have a 3rd level of pagetables for everything.
>>>>>> One could (correctly) argue it made *all* memory slower, but it does so
>>>>>> in a uniform fashion.
>>>>> 
>>>>> is it? I've seen during the memory self-test at boot that machines slow down noticably as they pass the 4G mark.
>>>> 
>>>> Not noticed that, and I can't see why it should be the case in general,
>>>> though I suppose some machines might be odd. Got any numbers?
>>> 
>>> just the fact that the system boot memory test takes 3-4 times as long with 8G or ram then with 4G of ram. I then boot a 64 bit kernel on the system and never use PAE mode again :-)
>>> 
>>> if you can point me at a utility that will test the speed of the memory in different chunks I'll do some testing on the Opteron systems I have available. unfortunantly I don't have any Xeon systems to test this on.
>> 
>> Mmm. 64-bit uniproc systems, with > 4GB of RAM, running a 32 bit kernel
>> don't really strike me as a huge market segment ;-)
> 
> true, but there are a lot of 32-bit uniproc systems sold by Intel that have (or can have) more then 4G of ram. These are the machines I was thinking of.

Does your opteron box have more than 1 socket? that'd explain it.

Anyway, it shouldn't happen on any normal platform. Until we get 
numbers that prove that it does (and understand why), I don't think
we need NUMA for PAE.

M.

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