[Paraview] pvserver always shows 100% cpu usage

[Jens]

Hi Paul,

I read the following on open-mpi-mailinglist:

"One issue is that "yield" might mean "yield if there is someone else
ready to run".  Like a traffic sign:  if someone else is there, you
yield.  If no one else is there, there's no way to tell that someone is
yielding.
Next, even if someone else is trying to run, "yield" doesn't give up the
CPU 100%.  It's still rather pesky."

so, to make is short: this is no solution :(

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
>                 _______________________________________________
>                 ParaView mailing list
>                 ParaView at paraview.org <mailto:ParaView at paraview.org>
>                 http://www.paraview.org/mailman/listinfo/paraview
> 
> 
> 
>     _______________________________________________
>     ParaView mailing list
>     ParaView at paraview.org <mailto:ParaView at paraview.org>
>     http://www.paraview.org/mailman/listinfo/paraview
> 
>