NAME

MPI_bufcopy_set - Set the local buffer copy size limit

SYNOPSIS

#include <mpi.h> 
int MPI_bufcopy_set(MPI_Aint size ); 
#include <pmpi.h> 
int PMPI_bufcopy_set(MPI_Aint size ); 

INPUT PARAMETER

size - size of the local buffer copy limit in bytes (integer)

DESCRIPTION

The MPI_bufcopy_set() function is used to set the default buffering maximum size of local (same machine inter-thread) sends for this rank. If the size of a send is below this limit, then this MPI implementation may attempt to allocate a temporary buffer to store the send's information. By copying into such buffers it is possible for sends to complete more rapidly. However, this uses up memory. If too many sends are outstanding, then memory could be exhausted.

If a send is too large then MPI will wait until a matching receive is posted. This requires only the amount of memory required to post an envelope to the destination rank, which at only 64 bytes, is trivially small.

By tuning this limit, it may be possible to improve performance at the cost of extra memory usage. The default size for this limit is 1 MiB.

Note that it is also possible to change this limit by using the MPI_BUFCOPY_SIZE environment variable. If set on process startup, this will set the default limit (in bytes) for all ranks on this machine.

This function is a non-portable extension of the MPI interface. It may not exist in other MPI implementations. PMPI_bufcopy_set() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error value. The the current MPI error handler is invoked if this return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

MPI_SUCCESS - No error.

SEE ALSO

MPI_bufcopy_get (3)

• Lockless
• MPI Documentation
• MPI_bufcopy_set