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From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2007-04-03 10:54:56

On Apr 3, 2007, at 9:07 AM, pooja_at_[hidden] wrote:

> Actually I am working on the course project in which I am running a
> huge
> computational intensive code.
> I am running this code on cluster.
> Now my work is to find out when does the process send control messages
> (e.g. compute process to I/O process indicating I/O data is ready)

By "I/O", do you mean stdin/stdout/stderr, or other file I/O?

If you mean stdin/stdout/stderr, this is handled by the IOF (I/O
Forwarding) framework/components in Open MPI. It's somewhat
complicated, system-level code involving logically multiplexing data
sent across pipes to sockets (i.e., local process(es) to remote

If you mean MPI-2 file I/O, you want to look at the ROMIO package; it
handles all the MPI-2 API for I/O.

Or do you mean "I/O" such as normal MPI messages (such as those
generated by MPI_SEND and MPI_RECV)? FWIW, we normally refer to
these as MPI messages, not really "I/O" (we typically reserve the
term "I/O" for file IO and/or stdin/stdout/stderr).

Which do you mean?

> and when does they send actual data (e.g I/O nodes fetching actual
> data
> that is to be transfered.)

This seems to imply that you're talking about parallel/network
filesystems. I have to admit that I'm now quite confused about what
you're asking for. :-)

> And I have to log the timing and duration in other file.

If you need to log the timing and duration of MPI calls, this is
pretty easy to do with the PMPI interface -- you can intercept all
MPI calls, log whatever information you want to log, invoke the
underlying MPI function to do the real work, and then log the duration.

> For this I need to know the States of Open MPi (Control messges)
> So that I can simply put print statements in Open MPi code and find
> out
> how it works.

I would [strongly] advise using a debugger. Printf statements will
only take you so far, and can be quite confusing in a parallel
scenario -- especially when they can alter the timing of the system
(i.e., Heisenburg kinds of effects).

> For this reason I was asking to know the state changes or atleast
> the way
> to find it out.

I'm still not clear on what state changes you're asking about.

 From this e-mail and your prior e-mails, it *seems* like you're
asking about how data gets from MPI_SEND in one process to MPI_RECV
in another process. Is that right?

If so, I would not characterize the code that does this as a state
machine in the traditional sense. Sure, as a computer program, it
technically *is* a state machine that changes states according to
assembly instructions, registers, etc., but we did not use generic
state machine abstractions throughout the code base. In many places,
there's simply a linear sequence of events -- not a re-entrant state

So if you're asking how a user message gets from MPI_SEND in one
process to MPI_RECV in another, we can describe that (it's a very
complicated answer that depends on many factors, actually -- it is
*not* a straightforward answer, not only because OMPI deals with many
device/network types, but also because there can be many variables
decided at run time that determine how a message is sent from a
process to a peer).

So before we go any further -- can you, as precisely as possible,
describe exactly what information you're looking for?

> Also my proff asked me to look into BTl transport layer to be used
> with
> MPi Api.

I described that in a prior e-mail.

Jeff Squyres
Cisco Systems