PCMPI#

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

Options Database Keys for the Server#

  • -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 all the linear systems solved by the MPI linear solver server

Options Database Keys for a specific KSP object

  • -[any_ksp_prefix]_mpi_linear_solver_server_minimum_count_per_rank - sets the minimum size of the linear system per MPI rank that the solver will strive for

  • -[any_ksp_prefix]_mpi_linear_solver_server_always_use_server - use the server solver code even if the particular system is only solved on the process (for debugging and testing purposes)

Notes#

The options database prefix for the actual solver is any prefix provided before use to the original KSP with KSPSetOptionsPrefix(), mostly commonly no prefix is used.

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

When the program is running with a single MPI process then it directly uses the provided matrix and right hand side and does not need to distribute the matrix and vector to the various MPI processes; thus it incurs no extra overhead over just using the KSP directly.

The solver options for actual solving 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.

Developer Note#

This PCType is never directly selected by the user, it is set when the option -mpi_linear_solver_server is used and the PC is at the outer most nesting of a KSP. The outer most KSP object is automatically set to KSPPREONLY and thus is not directly visible to the user.

See Also#

Using PETSc’s MPI parallel linear solvers from a non-MPI program, KSPCreate(), KSPSetType(), KSPType, KSP, PC, PCMPIServerBegin(), PCMPIServerEnd(), KSPCheckPCMPI()

Level#

developer

Location#

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

Examples#

src/ksp/ksp/tutorials/ex1.c

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