[Mpi3-tools] Next Tools WG Meeting 8/23 - MPIR & MPIT

[Martin Schulz]

Hi all,

Our next tools WG meeting is (as usual) on Monday 8/23 (tomorrow) at  
8am PDT,
11am EDT, 5pm MSZ. Jeff created a Webex session for us, which is  
linked on the
tools Wiki. It is:

https://cisco.webex.com/ciscosales/j.php?ED=145066572&UID=0&PW=NMjcyNzAwZmU2&RT=MiMxMQ%3D%3D
Password: tools

We have two main item for the agenda: MPIR and MPIT.

MPIR: John requested some time to finish the discussion on the MPIR  
document before
we turn the document into a standard compliant Latex document and give  
it for to the
MPI forum forum for review (has to happen by the end of next week).

MPIT: I recently gave a presentation on MPIT to the tools community  
and I would like to
discuss the feedback from that meeting and its impact on the MPIT  
proposal. More detail
on this are below.

Talk to you tomorrow / Monday,

Martin



Feedback from the tools community on MPIT (based on CScADS discussions):
(for those of you who were at the CScADS workshop, please feel free to  
add)

Collection of use cases
	Current ideas in MPIT seem to match those use cases very well
	High/Low watermarks seen as quite useful
	Identification of exhausted resources important

Naming
	Several name changes suggested
	configuration variables -> control variables (as in OpenMP)
	Prefixes:
		MPIT_CTRLVARS_...
		MPIT_PERFVARS_...

Verbosity levels
	Why restrict verbosity from 1 to 5?
	Allow a query for the max. verbosity N and then allow levels 1-N

Initialization
	Suggestion to remove IsInitialized and IsFinalized
	(not useful if we can initialize MPIT multiple times)

Bias towards adding Fortran routines
	Need more feedback from the Fortran gurus in the MPI forum

Control variables
	Very strong wish to allow the setting of control variables
	In particular autotuning community is very interested and promised to
		write up several concrete use cases
	How to deal with setting the variables from multiple tools
		a) provide lock/unlock routines
		b) allow one tool to Initialize MPIT exclusively in MPIT_Init
		c) Do nothing and leave races up to tools/users
	How to deal with synchronizing variables
		Provide additional information during query:
			readonly - can never be set
			sync/nosync - shows whether a variables is synchronizing or not
			communicator - setting a synchronizing variables requires a global
				operation on this communicator
				(can be MPI_COMM_SELF for nosync variables)
		Set routine takes communicator as argument
			Must be called by all members of the communicator

Extensibility
	Very strong wish to have the option to extend this interface
	Tools should have the ability to provide new variables
	(this was brought up by several tools groups for various needs)

	Seen as essential (not just for Extensibility): Profiling routines  
for MPIT

	Would like to see a different iterator concept:
		change from iterators to a list of variables with an integer index
		(this fixes the type of the iterator)
		Query the number of variables and then provide query routines to ask
			for more information on each variable
		Restrictions: variables can not be removed or reordered, just added
		
	How to return query information:
		Return a struct instead of a list of arguments
		Cleaner ways to integrate new information in future versions
		Need separate MPIT version constant to guard extensions

	Ideally: would like to give MPI an address for a variable to watch  
and MPI
		would then integrate this variable into the MPIT variables
		-> easy extension for new variables by external tools through same API

	Alternatively: tools can hide this in an PMPIT layer, but then need  
additional
		mechanisms to allocate "dummy" handles to avoid duplicating the  
handle space


		




________________________________________________________________________
Martin Schulz, schulzm at llnl.gov, http://people.llnl.gov/schulzm
CASC @ Lawrence Livermore National Laboratory, Livermore, USA



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