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Subject: Re: [OMPI users] Very slow MPI_GATHER
From: Pinero, Pedro_jose (Pedro_jose.Pinero_at_[hidden])
Date: 2012-03-01 03:33:30

Thank you for your fast response.


I am launching 200 light processes in two computers with 8 cores each
one (Intel i7 processor). They are dedicated and are interconnected
through a point-to-point Gigabit Ethernet link.


I read about oversubscribing nodes in the open-mpi documentation, and
for that reason I am using the option


- Mca mpi_yield_when_idle 1








>>On Feb 29, 2012, at 11:01 AM, Pinero, Pedro_jose wrote:


>> I am using OMPI v.1.5.5 to communicate 200 Processes in a 2-Computers
cluster connected though Ethernet, obtaining a very poor performance.


>Let me making sure I'm parsing this statement properly: are you
launching 200 MPI processes on 2 computers? If so, do >those computers
each have 100 cores?


>I ask because oversubscribing MPI processes (i.e., putting more than 1
process per core) will be disastrous to >performance.


>> I have measured each operation time and I haver realised that the
MPI_Gather operation takes about 1 second in each >>synchronization
(only an integer is send in each case). Is this time range normal or I
have a synchronization >>problem? Is there any way to improve this


>I'm afraid I can't say more without more information about your
hardware and software setup. Is this a dedicated HPC >cluster? Are you
oversubscribing the cores? What kind of Ethernet switching gear do you
have? ...etc.



>Jeff Squyres


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