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 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