Hello, The standard talks about the motivation of MPI_T as "MPI implementations often use internal variables to control their operation and performance. Understanding and manipulating these variables can provide a more efficient execution environment or improve performance for many applications." I could imagine that through performance variables, users can know MPI internal states during application execution. But how to use that to improve performance? What EXTRA advantages does MPI_T bring? I don't get the idea. Can someone shed light on that? Thank you. --Junchao Zhang