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Subject: Re: [OMPI devel] kernel 2.6.23 vs 2.6.24 - communication/wait times
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-04-12 16:34:06


On Apr 12, 2010, at 11:10 AM, Oliver Geisler wrote:

> > Is the /tmp filesystem on NFS by any chance?
>
> Yes, /tmp is on NFS .. those are diskless nodes all without disks and
> no swap space mounted.

Ah, that could do it. Open MPI's shared memory files are under /tmp. So if /tmp is NFS, you could get extremely high latencies because of dirty page writes out through NFS.

You don't necessarily have to make /tmp disk-full -- if you just make OMPI's session directories go into a ramdisk instead of to NFS, that should also be sufficient.

-- 
Jeff Squyres
jsquyres_at_[hidden]
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