[Bug 515496] [NEW] openmpi slows down whole system on Karmic

[Emmanuel FARHI]

Public bug reported:

Using a Karmic 8 cores system with shared memory, any MPI computation with openmpi 1.3 puts extreme load on the system, which affects the 'user experience' : the whole system gets stuck and very slow to respond. Such behaviors where not found with previous Ubuntu releases (8.04. 8.10, 9.04) where the usage of the system was not noticeably affected, while 100 % of the machine was indeed running on computations.
This may be related to changes in the kernel itself, as openmpi 1.3 was already used on Jaunty, without problems. 
When the OnDemand kernel load manager service is active, the cores are not equivalent, and some remain at 20% load, which desynchronize the MPI computation. The 'user experience' is still slightly better.
Unactivating the OnDemand kernel load manager service, all cores work equally, and computation is performed, but systems is nearly halted (very few resources remain for the system and the window manager).

In addition, openmpi 1.3 also suffers bug
<https://bugs.launchpad.net/ubuntu/+source/openmpi/+bug/504659> on
Karmic which does not make it a good solution for high demanding
computing.

Source: openmpi
Binary: openmpi-bin libopenmpi-dev libopenmpi1.3 openmpi-common openmpi-doc 
libopenmpi-dbg
Architecture: amd64
Version: 1.3.2-3ubuntu1.1
Distribution: karmic

** Affects: openmpi (Ubuntu)
     Importance: Undecided
         Status: New

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openmpi slows down whole system on Karmic
https://bugs.launchpad.net/bugs/515496
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