TotalView Users Guide - CI Wiki

Debugging Global Arrays Applications
it was stored in shared memory. All details of the data distribution, addressing,
and data access are encapsulated in the global array objects. Information
about the actual data distribution and locality can be easily obtained
and taken advantage of whenever data locality is important. The primary
target architectures for which GA was developed are massively-parallel distributed-memory
and scalable shared-memory systems.
GA divides logically shared data structures into “local” and “remote” portions.
It recognizes variable data transfer costs required to access the
data depending on the proximity attributes. A local portion of the shared
memory is assumed to be faster to access and the remainder (remote portion)
is considered slower to access. These differences do not hinder the
ease-of-use since the library provides uniform access mechanisms for all
the shared data regardless where the referenced data is located. In addition,
any processes can access a local portion of the shared data directly/
in-place like any other data in process local memory. Access to other portions
of the shared data must be done through the GA library calls.
GA was designed to complement rather than substitute for the messagepassing
model, and it allows the user to combine shared-memory and
message-passing styles of programming in the same program. GA inherits
an execution environment from a message-passing library (w.r.t. processes,
file descriptors etc.) that started the parallel program.
TotalView supports Global Arrays on the Intel IA-64 platform. You debug a
Global Arrays program in basically the same way that you debug any other
multi-process program. The one difference is that you will use the Tools >
Global Arrays command to display information about your global data.
The global arrays environment has a few unique attributes. Using TotalView,
you can:
� Display a list of a program's global arrays.
� Dive from this list of global variables to see the contents of a global array
in C or Fortran format.
� Cast the data so that TotalView interprets data as a global array handle.
This means that TotalView displays the information as a global array.
Specifically, casting to $GA forces the Fortran interpretation; casting to
$ga forces the C interpretation; and casting to $Ga tells TotalView to use
the language in the current context.
Within a Variable Window, the commands that operate on a local array, such
as slicing, filtering, obtaining statistics, and visualization, also operate on
global arrays.
The command you use to start TotalView depends on your operating system.
For example, the following command starts TotalView on a program
that is invoked using prun and which uses three processes:
totalview prun -a -N 3 boltz.x
Before your program starts parallel execution, TotalView asks if you want to
stop the job. (See Figure 104 on page 150.)
Choose Yes if you want to set breakpoints or inspect the program before it
begins execution.
TotalView Reference Guide: version 8.7 149