Measuring Communication and Computation Overlap
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Measuring Pure Communication Time
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallgather
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallgather_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallgatherv
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallgatherv_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallreduce
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iallreduce_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ialltoall
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ialltoall_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ialltoallv
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ialltoallv_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ibarrier
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ibarrier_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ibcast
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ibcast_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Igather
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Igather_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Igatherv
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Igatherv_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ireduce
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ireduce_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ireduce_scatter
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Ireduce_scatter_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iscatter
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iscatter_pure
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iscatterv
                                                    
                                                    
                                                
                                                    
                                                    
                                                        Iscatterv_pure
                                                    
                                                    
                                                
                                            
                                        Exchange
Exchange is a communication pattern that often occurs in grid splitting algorithms (boundary exchanges). The group of processes is similar to a periodic chain, and each process exchanges data with both left and right neighbor in the chain.
The turnover count is four messages per sample (two in, two out) for each process.
For two Isend messages, separate buffers are used.
Exchange Definition
| Property | Description | 
|---|---|
| Measured pattern | As symbolized between  | 
| MPI routines | MPI_Isend/MPI _Waitall, MPI_Recv | 
| MPI data type | MPI_BYTE | 
| Reported timings | time=Δt (in μsec) | 
| Reported throughput | 4X/time | 
Exchange Pattern
 
 
    in the figure below.
 in the figure below.