Internal LAM buffering is not going to be your big issue here; aside
from some MPI_Request and associated data structures, LAM doesn't
really allocate much per message. More specifically, the overhead for
each message is essentially constant, regardless of size. Whenever
possible, LAM will try to receive directly into your buffer (the
exceptions are small messages on low-latency networks like IB and GM).
So posting a lot of receives is not going to dramatically increase the
memory usage in LAM itself -- it's going to increase your process'
memory usage, because assumedly you have unique message buffers
associated with each of those requests.
Make sense?
You can't really monitor the internals of LAM/MPI itself, but you can
monitor the entire process with getrusage(). See the man page for
details.
On Nov 8, 2005, at 9:43 AM, Michael Lees wrote:
> Hi all,
>
> I'm trying to understand lam performance, in particular the overhead
> associated with communication.
> I have a simple program with 17 mpi processes, 16 of the processes
> (call
> them slaves) operate in cycles of message generation. Each cycle begins
> with the process sleeping for 100 miliseconds and then waking and
> sending 6 messages to the single master node.
> This results in the master receiving a burst of 16*6 messages every 100
> milliseconds. All the communication uses asynchronous sends and
> receives. Ideally I'd like all 96 messages of a cycle to be received
> before the next cycle starts.
>
> Is there anyway I can monitor the size of the internal lam buffers and
> their current usage. I want to try and figure out the maximum number of
> messages that I can send and receive reliably within the 100
> milliseconds period.
>
>
> Thanks
>
> --
> Michael Lees
>
>
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--
{+} Jeff Squyres
{+} The Open MPI Project
{+} http://www.open-mpi.org/
|
