Reading further into the article there is something about the IBM mpi
implementation
" The default interval for handling communication calls is 400
milliseconds."
Does lam have a similar default? And do I understand this correctly?
Is this the time between making subsequent checks on a blocking
communication?
ie., in MPI_Recv does it check for matching send and then sleep for 400
miliseconds?
Michael Lees wrote:
> Hi all,
>
>
> Does lam use polling or interrupts for its synchronous sending and
> receiving?
> Is it configurable to use either? If so what is the default behaviour?
>
> I have a thread for performing asynchronous sending and receiving,
> something along the lines of...
>
> while(running){
> MPI_IRecv(&request)
> While(recvflag ==0){
> MPI_Test(request,recvflag)
> MPI_Send()
> yield()
> }
> yield()
> }
>
> From reading a bit [1]:
> <snip>
> # Applications which have the following characteristics may see
> performance improvements when using with interrupt mode:
>
> * Applications that use nonblocking send or receive operations for
> communication.
>
> * Applications that have non-synchronized sets of send or receive
> pairs. In other words, the send from node0 is issued at a different
> point in time with respect to the matching receive in node1.
>
> * Applications that do not issue waits for nonblocking send or
> receive operations immediately after the send or receive, but rather do
> some computation prior to issuing the waits.
> </snip>
>
>
> Now my application seems to satisfy all three of these, will I have
> improved performance using interrupts?
> I have particular problems when there are multiple mpi processes per
> node. If you have a lot of MPI processes per node will interrupts
> perform better?
>
> Thanks
>
>
> [1] (http://www.llnl.gov/computing/tutorials/mpi_performance/)
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