On 08/17/2013 02:11 PM, William Gropp wrote:
MPI, where it implements the performance variables, doesn't need to store more than one - only in the session structure would there be copies.
I think you are saying the same thing I wrote in my email.
I view (without having participated) the design of the session as a place to put all of the overhead out of the critical path, including potential thread safety overheads. My comment about a high quality implementation is that it is possible, with good and careful design, to avoid most of the extra costs in the case of a single active session (probably one indirection and a branch).
Yes, of course. The single session case is easy. In fact, depending on how many variables we have, the multi-session case might not be too expensive either. I was just checking to make sure my understanding was correct. -- Pavan -- Pavan Balaji http://www.mcs.anl.gov/~balaji