[Mpi3-tools] Current Version of the MPIR document

[Ashley Pittman]

On 14 Jun 2010, at 17:27, Martin Schulz wrote:

> Hi all,
> 
> Attached is the latest and updated version of the MPIR document, which John
> DelSignore put together. The intent is still to publish this through the MPI forum
> as an official document. The details for this are still tbd. and Jeff will lead a
> discussion on this topic during the forum this week.

I think this is a good document and a huge step forward, I've learnt a few things I hadn't realised about the interface before.

Largely I'm in agreement with the document but I disagree with some parts of and would like clarification on a few aspects of MPIR_PROCDESC.

Section 9.2

Like the original work this document specifies a definition for MPIR_PROCDESC, it however then goes on to say that the definition isn't fixed but rather is up to the implementation.

typedef struct {
  char *host_name;
  char *executable_name;
  int pid;
} MPIR_PROCDESC;

Section 9.2 paragraph 4:
The pid member is the integer process identifier of the MPI process. Note that historically pid was defined as a C language int, which is an integer of an unknown size, which might be smaller than the size of a process identifier for the target system. Implementations should define pid as an integer size that is large enough to hold a process identifier for the target system. For example, implementations should use pid_t as the type of pid provided that pid_t is an integer type.

Are there MPI librarys in existence which don't use int as the type for pid?  I've certainly not seen any and never seen it necessary to read the type of MPIR_PROCDESC because it's type is well specified.  Actually MPICH2 tried changing this recently from a int to a long and I made them change it back.

Following on from this I don't believe that section 4.1 applies, or at least not as strictly as it's written currently.  It's possible to extract the information from the starter process without the debug information being present.

Ashley.

-- 

Ashley Pittman, Bath, UK.

Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk