MPI Tracing Data (Sun Studio 12: Performance Analyzer)

Sun Studio 12: Performance Analyzer

MPI Tracing Data

The Collector can collect data on calls to the Message Passing Interface (MPI) library. Currently, MPI tracing is only available for system running the Solaris OS. The functions for which data is collected are listed below.

`MPI_Allgather`	`MPI_Allgatherv`	`MPI_Allreduce`
`MPI_Alltoall`	`MPI_Alltoallv`	`MPI_Barrier`
`MPI_Bcast`	`MPI_Bsend`	`MPI_Gather`
`MPI_Gatherv`	`MPI_Irecv`	`MPI_Isend`
`MPI_Recv`	`MPI_Reduce`	`MPI_Reduce_scatter`
`MPI_Rsend`	`MPI_Scan`	`MPI_Scatter`
`MPI_Scatterv`	`MPI_Send`	`MPI_Sendrecv`
`MPI_Sendrecv_replace`	`MPI_Ssend`	`MPI_Wait`
`MPI_Waitall`	`MPI_Waitany`	`MPI_Waitsome`
`MPI_Win_fence`	`MPI_Win_lock`

MPI tracing data is converted into the following metrics.

Table 2–4 MPI Tracing Metrics


Metric	Definition
MPI Receives	Number of receive operations in MPI functions that receive data
MPI Bytes Received	Number of bytes received in MPI functions
MPI Sends	Number of send operations in MPI functions that send data
MPI Bytes Sent	Number of bytes sent in MPI functions
MPI Time	Time spent in all calls to MPI functions
Other MPI Calls	Number of calls to other MPI functions

The number of bytes recorded as received or sent is the buffer size given in the call. This number might be larger than the actual number of bytes received or sent. In the global communication functions and collective communication functions, the number of bytes sent or received is the maximum number, assuming direct interprocessor communication and no optimization of the data transfer or retransmission of the data.

The functions from the MPI library that are traced are listed in Table 2–5, categorized as MPI send functions, MPI receive functions, MPI send and receive functions, and other MPI functions.

Table 2–5 Classification of MPI Functions Into Send, Receive, Send and Receive, and Other


Category	Functions
MPI send functions	`MPI_Bsend`, `MPI_Isend`, `MPI_Rsend` , `MPI_Send`, `MPI_Ssend`
MPI receive functions	`MPI_Irecv`, `MPI_Recv`
MPI send and receive functions	`MPI_Allgather`, `MPI_Allgatherv`, `MPI_Allreduce`, `MPI_Alltoall`, `MPI_Alltoallv`, `MPI_Bcast`, `MPI_Gather`, `MPI_Gatherv`, `MPI_Reduce`, `MPI_Reduce_scatter`, `MPI_Scan`, `MPI_Scatter`, `MPI_Scatterv`, `MPI_Sendrecv`, `MPI_Sendrecv_replace`
Other MPI functions	`MPI_Barrier`, `MPI_Wait`, `MPI_Waitall` , `MPI_Waitany`, `MPI_Waitsome`, `MPI_Win_fence`, `MPI_Win_lock`

Collecting MPI tracing data can help you identify places where you have a performance problem in an MPI program that could be due to MPI calls. Examples of possible performance problems are load balancing, synchronization delays, and communications bottlenecks.