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Subject: Re: [OMPI users] machines swapping in running job[Scanned]
From: Arif Ali (aali_at_[hidden])
Date: 2008-05-07 12:08:14


Jeff Squyres wrote:
> Arif --
>
> Sorry for the delay in replying.
>
> Believe it or not, almost this exact issue just came up with the IBM
> Benchmark Center; they were using Open MPI with MPIRandomAccess and
> experiencing problems with running out of memory. We didn't get a
> full set of data and experiments run; it was somewhat odd that the
> problem seemed to happen most often with the Intel compilers
> (preliminary tests shows that we couldn't replicate the problem with
> the gcc compiler on the same problem size).
>
> However, the IBM Benchmark Center engineers were able to get
> successful runs in by using the btl_openib_free_list_max MCA
> parameter. This parameter essentially limits how much space the
> lowest-level IB driver in OMPI uses for fragment lists (it's actually
> fairly complex as to what it exactly does and how it helps in this
> situation -- insert "waving hands" image here...). This parameter
> defaults to "infinite". Setting it to a finite value can allow
> MPIRandomAccess to complete; I believe that the IBC engineers used
> values of 2000 and 4000 for their systems.
>
thanks, that's great, that worked

we are also using IBM machines (IBM x3455) but we are using the gcc
compiler that comes default with SLES 10

I have successfully run the HPCC using values 2048, 4096 and 8192; I
have kept this now at 2048 and continue testing.

Is it better if this value to be high or low?

regards,

-- 
Arif Ali
Software Engineer
OCF plc
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