Capturing Message Time

I am having difficulty finding the time is takes to send a message via MPI from one processor to another. The difficult step here is that these processors are of different architectures. They are connected via a network.

I am looking just for the time it takes to send a message. I've tried a few different things, but I'm just getting bad results.

Any ideas for how this can be done? Whenever I Google it, I get a bunch of sites that just have information on the function MPI_Wtime(), which is what I have been using.

MPI_Wtime
Is your 'time' synchronised?

Yes, I believe so.

I guess the issue I'm trying to work out is the concurrency of the situation.

The idea I've been using is essentially:

Code:

---


if(myrank == 0){
  start_time = MPI_WTIME
  SEND_MSG
}

if(myrank != 0){
  RECEIVE_MSG
}

if(myrank == 0){
    end_time = MPI_WTIME
}

---

And the idea I had was that once I arrived at the third 'if' statement, the message must have been received and I'd log the time. However, I do not believe this is correct. I don't think I am considering the concurrency of the code here.

So, my question is, on a high level - how do I log the communication time between these processors when I am using different processes, different architectures, and MPI for communication.

One idea I had was to do the MPI send and receive in a separate function and then wrap the MPI_WTIMEs around that function. However, I do not believe that is correct either.

Any ideas?

You know, I'm wondering if it is enough to measure just the time it takes to send a message?

Perhaps I am making this problem out to be more difficult than it is.

For example:

Code:

---

start_time = MPI_WTIME
SEND_MSG
end_time = MPI_WTIME

---

Would this give me the communication time for a message sent between two processors?

I am assuming that when the SEND_MSG function is finished the message is sent. So instead of trying to start the measuring timer on the sending processor and ending the message timer on the receiving processor, I can just measure around the send function and that is how long it took to send - or communicate - the message.

Is this logic sound? If so, my problem has become much, much easier!