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 CR module effectively allows application-level checkpointing
by invoking user-specified functions at the Checkpoint, Continue, and
Restart phases of LAM/MPI C/R support.
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: foo_checpkoint(), foo_continue(),
and 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 abort. Finally, the usual priority SSI parameter is
also available:
cr_self_priority
self's default priority is 25.
SEE ALSO
lamssi(7), mpirun(1), LAM User's Guide