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Subject: Re: [OMPI users] 2 to 1 oversubscription
From: Robert Kubrick (robertkubrick_at_[hidden])
Date: 2009-07-14 20:14:12


Jody,

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

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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