Ubuntu Manpage: lamtrace - Unload LAM trace data.

Provided by: lam-runtime_7.1.4-7.1build2_amd64

NAME

       lamtrace - Unload LAM trace data.

SYNOPSIS


       lamtrace [-hkvR] [-mpi] [-l listno] [-f #secs] [filename] [nodes] [processes]

OPTIONS

       -h            Print useful information on this command.

       -k            Copy and do not remove trace data.

       -v            Be verbose.

       -R            Delete all trace data from the specified nodes.

       -l            Unload only from the given list number.

       -mpi          Unload trace data for an MPI application.

       -f #secs      Signal  target processes to flush trace data to the daemon.  Then wait #secs before unload‐
                     ing.

       filename      Place trace data into this file (default: def.lamtr).

DESCRIPTION

The -t option of mpirun(1) and loadgo(1) allows the application to generate execution traces. These
traces are first stored in a buffer within each application process. When the buffer is full and when
the application terminates, the runtime buffer is flushed to the trace daemon (a structural component
within the LAM daemon). The trace daemon will also collect data up to a pre-compiled limit. Beyond this
limit, the oldest traces in will be forgotten in favor of the newer traces.

After an application has finished, the record of its execution is stored in the trace daemons of each
node that was running the application. The lamtrace command can be used to retrieve these traces and
store them in one file for display by a performance visualization tool, such as xmpi(1). If the applica‐
tion was started by xmpi(1), lamtrace is not normally needed as the equivalent functionality is invoked
with a button.

Incomplete trace data can be unloaded while the application is running. The output file must not exist
prior to invoking lamtrace. This is a good situation to use the -k option, which preserves the trace
daemon's contents after unloading. Each reload will then get the entire run's trace data up to the
present time.

A running process is likely to be holding the most recent trace data in an internal buffer. A standard
LAM signal, LAM_SIGTRACE (see doom(1)), causes trace enabled processes to flush the internal trace buffer
to the daemon. The -f option tells lamtrace to send this signal to all target processes before unloading
trace data. A race condition develops between the target process storing trace data to the daemon and
the unloading procedure. The problem is foisted upon the user who gives a delay parameter after -f.

Trace data are organized by node, process identifier and list number. A process can store traces on any
node, although the local node is the obvious, least intrusive choice. The process can identify itself in
any meaningful way (getpid(2) is a good idea) The list number is also chosen by the process. These val‐
ues may be set by an instrumented library, such as libmpi(3), or directly by the application with
lam_rtrstore(2). Unloading flexibility follows that of storing with the -l option selecting the list
number, and standard LAM command line mnemonics selecting nodes and processes.

Dropping old traces when a pre-compiled volume limit is reached only happens for positive list numbers.
Traces in negatively numbered lists will be collected until the underlying system runs out of memory. Do
not use negative list numbers for high volume trace data.

If no process selection is given on the command line, trace data will be unloaded for all processes on
each specified node.

LAM, its trace daemon and lamtrace are all unaware of the format and meaning of traces.

The -R option does not unload trace data. It causes the target trace daemons to free the memory occupied
by trace data in the given list. If all lists are specified (no -l option), the trace daemon is effec‐
tively reset to its state after initiating LAM.

Unloading MPI Trace Data
A special capability, selected by the -mpi option, exists to search for and unload only the trace data
generated by an MPI application. For this purpose, lamtrace is aware of the particular reserved list
numbers that libmpi(3) uses to store traces. It begins by searching all specified nodes and processes
(the whole LAM multicomputer, if nothing is specified) for a special trace generated by process rank 0 in
MPI_COMM_WORLD of an MPI application. This special trace contains the node and process identifiers of
all processes in that MPI_COMM_WORLD communicator. lamtrace then uses the node / process information to
collect all trace data generated by libmpi(3).

If multiple world communicators exist within LAM's trace daemons, the first one found is used. Multiple
worlds may be present due to multiple concurrent applications, trace data from a previous run not removed
(either with lamtrace or lamclean(1)), or an application that spawns processes. A particular world com‐
municator can be located by providing precise node and process location to lamtrace.

The -mpi option is not compatible with the -l option.

EXAMPLES

       lamtrace -v -mpi mytraces
           Unload  trace  data  into the file "mytraces" from the first MPI application found in a search of the
           entire LAM multicomputer.  Report on important steps as they are done.

       lamtrace n30 -l 5 p21367
           Unload trace data from list 5 of process ID 21367 on node 30.  Operate silently.

       lamtrace -mpi n30 p21367
           Unload trace data from the MPI application world group whose process rank 0 has PID 21367 and  is/was
           running on node 30.

BUGS

       Since trace data can be unloaded during an application's execution, there should be a way to incremental‐
       ly append to an output file.  This is a bit tricky with -mpi, but it can be done.

FILES

       def.lamtr     default output file