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Debugging Cray XT Applications
Debugging Cray XT Applications
The Cray XT Series is supported by the TotalView x86_64 distribution. This
section describes running applications on Cray XT Catamount. You should
be familiar with this information when running applications on a Cray XT
CNL. The primary difference between the two, and it is a big difference, is
that Cray XT CNL uses aprun to launch programs rather than yod.
Cray XT Catamount
On the Cray XT Catamount, all jobs running on compute nodes are started
with the yod starter program. These jobs do not have to be MPI jobs.
Debugging a program started with yod is similar to debugging any program
using a starter program. In general, you would type:
totalview totalview_args yod –a yod_args
For example:
totalview yod –a –np 4 ./my_prog
Here are some things you should know:
� tvdsvr_rs processes are started for your compute nodes. (This is a process
started by TotalView on a remote note that communicates back with
TotalView. For more information on this server, see Chapter 4.) yod will
then pass information to TotalView, which will then start the servers. If this
does not occur, consult your yod documentation.
� There may be more than one tvdsvr_rs process. TotalView will create one
tvdsvr_rs process for each RS_DBG_CLIENTS_PER_SERVER or 64 compute
nodes.
� To attach to a running program, attach to the instance of yod that is
controlling it using normal TotalView mechanisms. TotalView will automatically
attach to all compute node tasks that are part of the job.
� TotalView cannot know how many compute nodes are available, so each
server assumes that it will be serving 64 compute nodes, and asks for a
64-node license. You can override this default by using the
–nodes_allowed tvdsvr command-line option.
If you wish to use a small license (that is, a license for less than 64 processors),
you must use the –nodes_allowed tvdsvr command-line option.
The argument to this option specifies how many nodes the server supports
and how many licenses it needs. Because this is a tvdsvr_rs command-line
option, you must add it into the server launch string.
You can also use the –nodes_allowed server launch string option along with
the RS_DBG_CLIENTS_PER_SERVER environment variable to increase the
number of compute nodes each server will serve (and the number of Cray
licences it asks for). However, we do not recommend that you set this
server launch string option to a value greater than 256. (Note that you only
need set this variable if RS_DBG_CLIENTS_PER_SERVER is greater than 64.)
144 Chapter 7: Setting Up Parallel Debugging Sessions