[Paraview] pvserver always shows 100% cpu usage

[John M. Patchett]

Hi Jens,
    I would think that each pvserver process would have to be able to  
detect that it was in a lengthy wait state because it sure would suck  
to have an MPI_Wait in the middle of each send/recv pair during  
compositing ...  And it would probably be difficult to handle the  
tiled display communication.
The design of a solution might not be so straight forward ....  I  
think,  you would have to first decide that it really is a problem  
versus cost of doing business.
-John.

On Dec 5, 2008, at 9:53 AM, Jens wrote:

> Hi John,
>
> thought about this problem again...
>
> A solution could be
> a)to use MPI_IRecv/MPI_Wait instead of MPI_Recv.
>
> If that results in the same 100% cpu for the MPI_Wait-command,
> b) it could be a solution to add a wait()/sleep() just beweeen  
> MPI_IRecv
> and MPI_Wait.
> How long this wait/sleep would be could depend
> a) on the time the function MPI_Wait takes to return.
> b) or on some value send by process 0 (process 0 could send other
> processes to sleep for a while)
>
> What do you think?
>
> 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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>>