3.8 Extensions for Sequential Re-run of a Parallel Node

In some scenarios, a sequential re-run of a parallel node is desired. One example is instruction-level accurate architecture simulations, in which case the user may wish to repeat the execution of a node in a parallel run in the sequential simulator. AMPI provides support for such needs by logging the change in the MPI environment on a certain processors. To activate the feature, build AMPI module with variable ``AMPIMSGLOG'' defined, like the following command in charm directory. (Linking with zlib ``-lz'' might be required with this, for generating compressed log file.)

> ./build AMPI net-linux -DAMPIMSGLOG

The feature is used in two phases: writing (logging) the environment and repeating the run. The first logging phase is invoked by a parallel run of the AMPI program with some additional command line options.

> ./charmrun ./pgm +p4 +vp4 +msgLogWrite +msgLogRank 2 +msgLogFilename "msg2.log"

In the above example, a parallel run with 4 processors and 4 VPs will be executed, and the changes in the MPI environment of processor 2 (also VP 2, starting from 0) will get logged into diskfile "msg2.log".

Unlike the first run, the re-run is a sequential program, so it is not invoked by charmrun (and omitting charmrun options like +p4 and +vp4), and additional comamnd line options are required as well.

> ./pgm +msgLogRead +msgLogRank 2 +msgLogFilename "msg2.log"