lamssi_cr(7) LAM SSI CR OVERVIEW lamssi_cr(7)NAME
LAM SSI checkpoint / restart - overview of LAM's MPI checkpoint /
restart SSI modules
DESCRIPTION
The "kind" for checkpoint / restart SSI modules is "cr". Specifically,
the string "cr" (without the quotes) is the prefix that should be used
with the mpirun command line with the -ssi switch. For example:
mpirun -ssi cr blcr C my_mpi_program
LAM/MPI can involuntarily checkpoint and restart parallel MPI jobs.
Doing so requires that LAM/MPI was compiled with thread support and
that back-end checkpointing systems are available at run-time. MPI
jobs will have to run with at least MPI_THREAD_SERIALIZED support. If
a job elects to run with checkpoint/restart support and an available cr
module is found, the job's thread level will automatically be promoted
to MPI_THREAD_SERIALIZED. See the User's Guide for more details.
Checkpoint Phases
LAM defines three phases for checkpoint / restart support in each MPI
process:
Checkpoint.
When the checkpoint request arrives, before the actual checkpoint
occurs.
Continue.
After a checkpoint has successfully completed, in the same process
as the checkpoint was invoked in.
Restart
After a checkpoint has successfully completed, in a new / restarted
process.
The Continue and Restart phases are identical except for the process in
which they are invoked -- the Continue phase is invoked in the same
process as the Checkpoint phase was invoked. The Restart phase is only
invoked in newly restarted processes.
AVAILABLE MODULES
LAM currently has two cr modules: blcr and self. In order for an MPI
job to be able to be checkpointed and restarted, all of its MPI SSI
modules must support checkpoint/restart. Currently, this means using
the crtcp RPI module or the gm RPI module when compiled with gm_get()
support (see the User's Guide for more details).
blcr CR Module
The Berkeley Lab Checkpoint/Restart (BLCR) single-node checkpointer is
a software system from Lawrence Berkeley Labs. See the project web
page for more details: http://www.nersc.gov/research/ftg/checkpoint/.
The blcr module has one SSI parameter:
cr_blcr_priority
blcr's default priority is 50.
self CR Module
The self module, when used with checkpoint/restart SSI modules, will
invoke the user-defined functions to save and restore checkpoints. It
is simply a mechanism for user-defined functions to be invoked at LAM's
Checkpoint, Continue, and Restart phases. Hence, the only data that is
saved during the checkpoint is what is written in the user's checkpoint
function. No MPI library state is saved at all.
As such, the model for the self module is slightly different than, for
example, the blcr module. Specifically, the Restart function is not
invoked in the same process image of the process that was checkpointed.
The Restart phase is invoked during MPI_INIT of a new instance of the
application (i.e., it starts over from main()).
Multiple SSI parameters are available:
cr_self_user_prefix
Specify a string prefix for the name of the checkpoint, continue,
and restart functions that should be invoked by LAM. That is,
specifying "-ssi cr_self_user_prefix foo" means that LAM expects to
find three functions at run-time: int foo_checkpoint(), int
foo_continue(), and int foo_restart(). This is a convenience
parameter that can be used instead of the three parameters listed
below.
cr_self_user_checkpoint
Name of the user function to invoke during the Checkpoint phase.
cr_self_user_continue
Name of the user function to invoke during the Continue phase.
cr_self_user_restart
Name of the user function to invoke during the Restart phase.
If none of these parameters are specified and the self module is
selected, it will use the default prefix lam_cr_self
Finally, the usual priority SSI parameter is also available:
cr_self_priority
self's default priority is 25.
SEE ALSOlamssi(7), mpirun(1), LAM User's Guide
LAM 7.1.5b2 June, 2008 lamssi_cr(7)
