Using the Attach Subset Command

When you are running a large MPI job, you may not want to TotalView to attach to each process as it starts. Instead, you may want to choose the processes to which TotalView should attach. This is exactly what the Group > Attach Subset command is for. Here's the dialog box displayed after you select this command:

Clicking on processes in the top part of dialog box changes the action from Attach to Detach or Detach to Attach. If the process is not yet started, TotalView will not attach to any process whose action is Detach. However, if TotalView is already attached to the process, it will detach itself from processes whose action is Detach.

The controls in the Filters area let you limit which processes TotalView automatically attaches to, as follows:

• The Communicator control lets you name that the processes must be involved with the communicators that you select. For example, if something goes wrong that involves one of your communicators, selecting it from the list tells TotalView to only attach to the processes that use it.
• The Talking to Rank control further limits the processes to those that you name here. Most of the entries in this list are just the process numbers. In most cases, you would select All or MPI_ANY_SOURCE.
• The three checkboxes in the Message Type area add yet another qualifier. Checking a box tells TotalView to only display communicators that are involved with a Send, Receive, or Unexpected message.

Many applications place values that indicate the rank in a variable so that the program can refer to them as they are needed. If you do this, you can display the variable in a Variable Window and then select the Tools > Attach Subset (Array of Ranks) command to display this dialog box.