[Mpi3-tools] MPIT_PERFORMANCE_ALL and layering

[Dave Goodell]

I think that we should reconsider including MPIT_PERFORMANCE_ALL as it  
currently exists in the MPIT proposal because it discourages libraries  
and layering among performance tools.  If you have two tool libraries  
and one or both of them use MPIT_PERFORMANCE_ALL to start/stop their  
performance variables, the tools are likely to be incompatible.  One  
of MPI's great strengths is providing support mechanisms for parallel  
libraries, I don't see why we should omit those mechanisms in the  
tools space.

I understand the convenience and (potentially) performance arguments  
to be made for having functionality like this, but we might want to  
consider scoping it sort of like we do for communicators.  Perhaps  
make it possible to group handles or open handles with an associated  
context of sorts to perform the group start/stop operations later.

Alternatively, if there is no substantial performance argument to be  
made, we could just drop MPIT_PERFORMANCE_ALL altogether.  A for-loop  
isn't particularly burdensome to tools/applications.

I don't have a concrete alternative proposal here, I just wanted to  
bring up the issue for discussion.  I unfortunately missed the last  
concall due to technical difficulties, so I wasn't able to bring it up  
there.

-Dave