On Mon, Mar 9, 2009 at 10:56 AM, Jeff Squyres <firstname.lastname@example.org
> It depends on the characteristics of the nodes in question. You mention the
> CPU speeds and the RAM, but there are other factors as well: cache size,
> memory architecture, how many MPI processes you're running, etc. Memory
> access patterns, particularly across UMA machines like clovertown and
> follow-in intel architectures can really get bogged down by the RAM
> bottlneck (all 8 cores hammering on memory simultaneously via a single
> memory bus).
> On Mar 9, 2009, at 10:30 AM, Sangamesh B wrote:
>> Dear Open MPI team,
>> With Open MPI-1.3, the fortran application CPMD is installed on
>> Rocks-4.3 cluster - Dual Processor Quad core Xeon @ 3 GHz. (8 cores
>> per node)
>> Two jobs (4 processes job) are run on two nodes, separately - one node
>> has a ib connection ( 4 GB RAM) and the other node has gigabit
>> connection (8 GB RAM).
>> Note that, the network-connectivity may not be or not required to be
>> used as the two jobs are running in stand alone mode.
>> Since the jobs are running on single node - no intercommunication
>> between nodes - so the performance of both the jobs should be same
>> irrespective of network connectivity. But here this is not the case.
>> The gigabit job is taking double the time of infiniband job.
>> Following are the details of two jobs:
>> Infiniband Job:
>> CPU TIME : 0 HOURS 10 MINUTES 21.71 SECONDS
>> ELAPSED TIME : 0 HOURS 10 MINUTES 23.08 SECONDS
>> *** CPMD| SIZE OF THE PROGRAM IS 301192/ 571044 kBYTES ***
>> Gigabit Job:
>> CPU TIME : 0 HOURS 12 MINUTES 7.93 SECONDS
>> ELAPSED TIME : 0 HOURS 21 MINUTES 0.07 SECONDS
>> *** CPMD| SIZE OF THE PROGRAM IS 123420/ 384344 kBYTES ***
>> More details are attached here in a file.
>> Why there is a long difference between CPU TIME and ELAPSED TIME for
>> Gigabit job?
>> This could be an issue with Open MPI itself. What could be the reason?
>> Is there any flags need to be set?
>> Thanks in advance,
> Jeff Squyres
> Cisco Systems
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