[Paraview] pvserver always shows 100% cpu usage

[Paul Edwards]

Hi all,

It just depends on how it is implemented with MPI.  There will be lower
latency if it spins in a loop waiting for a message.  Here is a link to the
FAQ which shows how you can stop this for OpenMPI:

http://www.open-mpi.org/faq/?category=running#oversubscribing
http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded

Regards,
Paul

2008/12/5 John M. Patchett <patchett at lanl.gov>

> Hi Jens,
>  If I recall correctly, your observation lies in the type of hardware you
> are using.   I think some hardware allows a developer to leverage an
> interrupt while some requires polling for a received message.   Design
> requirements for MPI to be fast with low latency usually (I presume)
> outweigh lowering heat production.
>
> I think I first noticed this issue with mvapich when infiniband was new.  I
> don't think we had it with Myrinet 2000 or Gig-E.
>
> I also think ParaView is a normal mpi application, we just don't notice
> machines spinning while waiting during batch processing, we just assume
> they're working hard.
>
>
> -John.
>
> On Dec 5, 2008, at 9:42 AM, Jens wrote:
>
>  Hi John,
>>
>> thanks for your answer. That makes sense. "Normal" mpi-apps are probably
>> not written to wait for more things to do - they are simply always busy.
>>
>> It is just a pity that the cluster has to run 100% producing a lot of
>> heat for nothing.
>>
>> So the MPI-lib will probably not change this behavior :( ? (I am using
>> open-mpi 1.2.8)
>>
>> Greetings
>> Jens
>>
>>
>> John M. Patchett schrieb:
>>
>>> Hi Jens,
>>>  Your pvserver is probably waiting on an MPI_Recv and your MPI
>>> implementation is spinning.
>>> You will note that process 0 probably isn't doing this, as the other
>>> nodes are waiting on process 0 to send.
>>> I have searched this problem all the way to the MPI developers as it's
>>> easy to replicate without paraview and the MPI guys assure me the
>>> alternatives are worse.
>>> -John.
>>>
>>> On Dec 5, 2008, at 8:42 AM, Jens wrote:
>>>
>>>  Hi,
>>>>
>>>> if I run "mpirun -np 4 ./pvserver" on our cluster-node and connect from
>>>> my client, this pvserver always shows 100% cpu usage - even if I do
>>>> nothing at the client.
>>>>
>>>> Seems to me as if there is a loop waiting for the client to ask for
>>>> action - but this loop is calling no wait/sleep function.
>>>>
>>>> Greetings
>>>> Jens
>>>> _______________________________________________
>>>> ParaView mailing list
>>>> ParaView at paraview.org
>>>> http://www.paraview.org/mailman/listinfo/paraview
>>>>
>>>
>>>
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