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Subject: Re: [OMPI users] kernel 2.6.23 vs 2.6.24 - communication/wait times
From: Oliver Geisler (openmpi_at_[hidden])
Date: 2010-04-06 13:46:36


On 4/1/2010 12:49 PM, Rainer Keller wrote:

> On Thursday 01 April 2010 12:16:25 pm Oliver Geisler wrote:
>> Does anyone know a benchmark program, I could use for testing?
> There's an abundance of benchmarks (IMB, netpipe, SkaMPI...) and performance
> analysis tools (Scalasca, Vampir, Paraver, Opt, Jumpshot).
>

I used SkaMPI to test communication: Most important the third column
showing the communication time. Same effect, kernel lower 2.6.24 showing
faster communication(by thousands) against higher kernel version with
slow communication.

Hm. The issue seems not to be linked to the application. The kernel
configuration was carried forward from the working kernel 2.6.18 thru to
2.6.33 mostly using defaults for new features.

Any ideas what to look for? What other tests could I make to give you
guys more information?

Thanks so far,

oli

Tested on Intel Core2 Duo with openmpi 1.4.1

"skampi_coll"-test

kernel 2.6.18.6:
# begin result "MPI_Bcast-length"
count= 1 4 1.0 0.0 16 0.1 1.0
count= 2 8 1.0 0.0 8 0.0 1.0
count= 3 12 1.0 0.0 16 0.0 1.0
count= 4 16 1.3 0.1 32 0.0 1.3
count= 6 24 1.0 0.0 8 0.2 1.0
count= 8 32 1.0 0.0 32 0.1 1.0
{...}
count= 370728 1482912 1023.8 42.3 8 1023.8 1023.1
count= 524288 2097152 1440.3 3.7 8 1440.3 1439.5
# end result "MPI_Bcast-length"
# duration = 0.09 sec

kernel 2.6.33.1:
# begin result "MPI_Bcast-length"
count= 1 4 1786.5 131.2 34 1095.3 1786.5
count= 2 8 1504.9 77.1 34 759.3 1504.9
count= 3 12 1852.4 139.2 35 1027.9 1852.4
count= 4 16 2430.5 152.0 38 1200.5 2430.5
count= 6 24 1898.7 69.5 35 807.6 1898.7
count= 8 32 1769.1 16.3 34 763.3 1769.1
{...}
count= 370728 1482912 216145.9 3011.6 29 216145.9 214898.1
count= 524288 2097152 274813.7 1519.5 12 274813.7 274087.4
# end result "MPI_Bcast-length"
# duration = 140.64 sec

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