PCMPI#

Calls an MPI parallel KSP to solve a linear system from user code running on one process

Options Database Keys#

  • -mpi_linear_solver_server - causes the PETSc program to start in MPI linear solver server mode where only the first MPI rank runs user code

  • -mpi_linear_solver_server_view - displays information about the linear systems solved by the MPI linear solver server

  • -pc_mpi_minimum_count_per_rank - sets the minimum size of the linear system per MPI rank that the solver will strive for

  • -pc_mpi_always_use_server - use the server solver code even if the particular system is only solved on the process, this option is only for debugging and testing purposes

Notes#

The options database prefix for the MPI parallel KSP and PC is -mpi_

The MPI linear solver server will not support scaling user code to utilize extremely large numbers of MPI ranks but should give reasonable speedup for potentially 4 to 8 MPI ranks depending on the linear system being solved, solver algorithm, and the hardware.

It can be particularly useful for user OpenMP code or potentially user GPU code.

When the program is running with a single MPI rank then this directly uses the provided matrix and right hand side (still in a KSP with the options prefix of -mpi) and does not need to distribute the matrix and vector to the various MPI ranks; thus it incurs no extra overhead over just using the KSP directly.

The solver options for KSP and PC must be controlled via the options database, calls to set options directly on the user level KSP and PC have no effect because they are not the actual solver objects.

When -log_view is used with this solver the events within the parallel solve are logging in their own stage. Some of the logging in the other stages will be confusing since the event times are only recorded on the 0th MPI rank, thus the percent of time in the events will be misleading.

See Also#

KSPCreate(), KSPSetType(), KSPType, KSP, PC, PCMPIServerBegin(), PCMPIServerEnd()

Level#

beginner

Location#

src/ksp/pc/impls/mpi/pcmpi.c

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Index of all PC routines
Table of Contents for all manual pages
Index of all manual pages