TotalView Users Guide - CI Wiki

Debugging Parallel Applications Tips
other parallel processes that have not yet arrived at the breakpoint. This
can cause a timeout.
To turn the option off, select the Process Window Action Point >
Properties command while the line with the stop symbol is selected. After
the Properties Dialog Box appears, select the Process button in the When
Hit, Stop area, and also select the Plant in share group button.
CLI: dbarrier location –stop_when_hit process
� Control the poe process
Even though the poe process continues under debugger control, do not
attempt to start, stop, or otherwise interact with it. Your parallel tasks
require that poe continues to run. For this reason, if poe is stopped,
TotalView automatically continues it when you continue any parallel task.
� Avoid slow processes due to node saturation
If you try to debug a PE program in which more than three parallel tasks
run on a single node, the parallel tasks on each node can run noticeably
slower than they would run if you were not debugging them.
In general, the number of processes running on a node should be the
same as the number of processors in the node.
This becomes more noticeable as the number of tasks increases, and, in
some cases, the parallel tasks does not progress. This is because PE uses
the SIGALRM signal to implement communications operations, and AIX
requires that debuggers must intercept all signals. As the number of parallel
tasks on a node increases, TotalView becomes saturated and can’t
keep up with the SIGALRM signals being sent, thus slowing the tasks.
130 Chapter 6: Setting Up MPI Debugging Sessions