[Paraview] pvserver always shows 100% cpu usage

[Jens]

Hi John,

I compared a)MPI_Send/MPI_Recv with b)MPI_ISend/MPI_IRecv/MPI_Wait and
it depends on the situation which style is the fastest - style b is not
simply worse than style a. If you have high latency because of your
network-hardware you are better of with style b. But it is difficult to
tell, because there is not much difference.

Anyway, is there one single part in the paraview-code, which handles the
MPI-Stuff, or is MPI all over the place? If first is the case, it would
be easy to implement some "wait"-packet+constant polling of process 0 to
get rid of MPI-lib-dependens, but processor and/or memory affinity is
probably a problem then ...
(http://www.open-mpi.org/faq/?category=tuning#using-paffinity)

Greetings
Jens

John M. Patchett schrieb:
> 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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>>>
>