lamssi_cr(7)							LAM SSI CR OVERVIEW						      lamssi_cr(7)

NAME

       lamssi_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  pro-
       moted 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, speci-
	   fying "-ssi cr_self_user_prefix foo" means that LAM expects to find three functions at run-time:  int  foo_checkpoint(),  int  foo_con-
	   tinue(), 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 ALSO

       lamssi(7), mpirun(1), LAM User's Guide

LAM 7.1.4							    July, 2007							      lamssi_cr(7)