Displaying the Message Queue Graph

TotalView can graphically display your MPI program's message queue state. If you select the Process Window's Tools > Message Queue Graph command, TotalView displays a window with a large empty area. After you select the ranks to be monitored, the kind of messages, and message states, TotalView updates this window to show the current queue state. For example:

Tools > Message Queue Graph Window

The numbers within the boxes indicate a process's rank. Diving on a box tells TotalView that it should open a Process Window for that process.

The numbers next to the arrows indicate the number of messages when TotalView created the graph. Diving on the arrow tells TotalView that it should display its Tools > Message Queue Window, which will have detailed information about the messages.

This graph shows you the state of your program at a particular instant. Selecting the Display button tells TotalView that it should update the display.

While you can use this window in many ways, here are some to consider:

• Pending messages often indicate that a process cannot keep up with the amount of work it is expected to perform. These messages indicate places where you may be able to improve your program's efficiency.
   
• Unexpected messages can indicate that something is wrong with your program because the receiving process does not know how to process the message.
   
• After a while, the shape of the graph tends to tell you something about how your program is executing. If something does not look right, you might want to determine why it looks different.
   
• You can change the shape of the graph by dragging either nodes or the arrows. This is often useful when you are comparing sets of nodes and their messages with one another. TotalView does not remember the places to which you have dragged the nodes and arrows. This means that if you select the Display button after you arrange the graph, your changes are lost.