[Paraview] pvserver always shows 100% cpu usage

[Jens]

Hi Paul,

this is a very good hint. Thanks a lot.
But is sadly does not work :(

I started pvdataserver like this:
	mpirun --mca mpi_yield_when_idle 1 -np 4 ./pvdataserver
and still see three processes with 100% cpu, while no-one is connected.

This happens on a Dell R805 (2xAMD QuadCore-Opteron) with CentOS 5.2,
OpenMPI 1.2.8 and Paraview 3.4.0 - all compiled with Intel 11.0.

Greetings
Jens


Paul Edwards schrieb:
> 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 <mailto: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
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