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Subject: Re: [OMPI devel] kernel 2.6.23 vs 2.6.24 - communication/wait times
From: Oliver Geisler (openmpi_at_[hidden])
Date: 2010-04-12 11:10:04


Quoting Ashley Pittman <ashley_at_[hidden]>:

>
> On 10 Apr 2010, at 04:51, Eugene Loh wrote:
>
>> Why is shared-memory performance about four orders of magnitude
>> slower than it should be? The processes are communicating via
>> memory that's shared by having the processes all mmap the same file
>> into their address spaces. Is it possible that with the newer
>> kernels, operations to that shared file are going all the way out
>> to disk? Maybe you don't know the answer, but hopefully someone on
>> this mail list can provide some insight.
>
> 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.

Maybe I should setup one of the nodes with a disk, so I could try the
difference.

(Sorry, but I may return results next week since, I am out of office
right now)

Thanks
oli

> Ashley,
>
> --
>
> Ashley Pittman, Bath, UK.
>
> Padb - A parallel job inspection tool for cluster computing
> http://padb.pittman.org.uk
>
>
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