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Subject: Re: [OMPI users] 2 to 1 oversubscription
From: Klymak Jody (jklymak_at_[hidden])
Date: 2009-07-14 21:03:58


On 14-Jul-09, at 5:14 PM, Robert Kubrick wrote:

> Jody,
>
> Just to make sure, you did set processor affinity during your test
> right?

I'm not sure what that means in the context of OS X.

Hyperthreading was turned on.

Cheers, Jody

>
> On Jul 13, 2009, at 9:28 PM, Klymak Jody wrote:
>
>> Hi Robert,
>>
>> I got inspired by your question to run a few more tests. They are
>> crude, and I don't have actual cpu timing information because of a
>> library mismatch. However:
>>
>> Setup:
>> Xserve, 2x2.26 GHz Quad-core Intel Xeon
>> 6.0 Gb memory 1067 MHz DDR3
>> Mac OS X 10.5.6
>>
>> Nodes are connected with a dedicated gigabit ethernet switch.
>>
>> I'm running the MITgcm, a nonhydrostatic global circulation model.
>> The grid size is modest: 10x150x1600, so bear that in mind.
>> Message passing is on the dimension that is 150x10, and typically
>> is 3 grid cells in either direction. I'm not sure how many
>> variables are passed, but I would guess on the order of 24.
>>
>> I turned off all the I/O I knew of to reduce disk latency.
>>
>> 1 node: 8 processes: 54 minutes
>> 1 node: 16 processes: 40 minutes (oversubscribed)
>> 2 nodes, 16 processes: 29 minutes
>>
>> So, oversubscribing was faster (in this case), but it didn't double
>> the speed. Certainly spreading the load to another node was much
>> faster.
>>
>> I haven't had a chance to implement Warner's suggestion of turning
>> hyperthreading off to see what affect that has on the speed.
>>
>> Cheers, Jody
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>
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