Hi George, However, the effect on tools is not limited to global objects such as the predefined communicators - the semantics are changed for *any* communicator on which these info assertions are set. Your "and tools" bit is therefore necessary but not sufficient. I believe Jim has now changed the wording of the sentence you are concerned about back to a previous version, i.e. "The usage of info hints may also impact the effectiveness of tools." Does that alleviate your concern? Cheers, Dan. On 09/02/2016 22:36, George Bosilca wrote:

Sorry to jump in the middle (or the end) of the discussion. From my "MPI user" point of view, the last part of the proposed advice is unsettling.

"The usage of some info hints may allow the MPI library to change its behavior and, as a result, impact the effectiveness of tools."

seems to have a broader scope, and includes application developers, when the most obvious target should have been tools developers. I think removing the last part and emphasizing tools and libraries, makes a more clear point.

"Setting info hints on the predefined communicators \const{MPI\_COMM\_WORLD} and \const{MPI\_COMM\_SELF} may have unintended effects, as changes to these global objects may affect all components of the application, including libraries and tools."

George.

On Tue, Feb 9, 2016 at 8:02 PM, Jim Dinan <[email protected] <mailto:[email protected]>> wrote:

We're calling the proposal "info assertions", but the standard still refers to them as "hints".

Reading the proposed change again, I think it might be helpful (and more fair to tools) to say why info could impact tools:

Setting info hints on the predefined communicators \const{MPI\_COMM\_WORLD} and \const{MPI\_COMM\_SELF} may have unintended effects, as changes to these global objects may affect all components of the application, including libraries. The usage of some info hints may allow the MPI library to change its behavior and, as a result, impact the effectiveness of tools.

~Jim.

On Tue, Feb 9, 2016 at 12:38 PM, Daniel Holmes <[email protected] <mailto:[email protected]>> wrote:

Hi Jim,

I like that change. On a side note: are we really still calling them "info hints" in this context rather than "info assertions"?

Cheers, Dan.

On 09/02/2016 15:51, Jim Dinan wrote:

...

Hi All,

I'm preparing the updated draft of info assertions for a reading in March. Where did we land on an advice regarding tools? Do we want advice (1) to users, that they info keys may impact tools and/or (2) to tools that they should check info?

For instance, we could extend the current advice with the following sentence:

Setting info hints on the predefined communicators \const{MPI\_COMM\_WORLD} and \const{MPI\_COMM\_SELF}may have unintended effects, as changes to these global objects may affect all components of the application, including libraries. The usage of info hints may also impact the effectiveness of tools.

~Jim.

On Fri, Dec 18, 2015 at 5:24 AM, Marc-Andre Hermanns <[email protected] <mailto:[email protected]>> wrote:

Hi Jeff,

> at the moment we don't handle MPI_THREAD_MULTIPLE at all. But we want > to get there ;-) > > > You should vote for endpoints, as this may help you out here, > particularly if users start mapping endpoints 1:1 w/ threads.

That would certainly ease things for us in these situations. Unfortunately endpoints force use to adapt other infrastructure in our measurement system.

> b) Creating a derived datatype on the fly to add tool-level data to > the original payload may induce a large overhead in practically > _every_ send & receive operation and perturb the measurement. > > > You should evaluate this experimentally. I wrote a simple test > (https://github.com/jeffhammond/BigMPI/blob/master/test/perf/typepiggy.c) > and measured 1.5 us per call of overhead to create a datatype. That > is not significant except for very small messages.

Thanks for the pointer. You are right. I should evaluate this further. 1.5us does indeed seem tolerable. I wonder how the influence of the derived datatype is on overall messaging performance, though.

This is also something I should evaluate in the process.

Cheers, Marc-Andre

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