Newsgroups: comp.parallel.pvm
From: destri@doncarlos.eng.unipr.it(Giulio Destri)
Subject: Barrier time problems in Fortran
Organization: Dipartimento di Ingegneria dell'Informazione
Date: 24 Jan 1995 11:43:02 GMT
Message-ID: <3g2p46$sl9@sirio.cineca.it>

Hello Everybody,

We are trying to port a very intensive Fortran program from
the Cray T3D (Cray PVM) to a workstation cluster (Public Domain
PVM version 3.3.6), operating in a SunOs 4.1.2 and 4.1.3 environment.
The problem we have found is the incorrect working of the PVM
barrer calls, when the execution times of the single processes
(tasks) are high.
Operating on different hosts (e.g. SPARC-20 vs SPARC-2), with
different workload, and the necessity to access critical resources
(e.g. buses) force identical tasks to have different execution
times. The waiting times at a barrier can be very high for the
first processes arriving at this point of execution.
The stop in the processing phase seems to have no explanations from the
point of view of the Operating System.
So the stopped projects are "swapped out" from the memory active area.
When the lowest processes finally arrive at barrier point, all the
processes can be released from block.
The last arrived processes can continue their running but the others
can not be recalled in active memory.
In this way at the next barrier only some tasks can arrive, and the
system enters in a permanent blocking wait state.

We would like to know:
a. Is our diagnosis correct?
b. Are there some variables to be set during compilation or execution
   phase of a similar PVM program?
c. Have we to write a different construct to enhance the simple barrier
   call?
d. Do some solutions internal to PVM exist?
e. Have we to add some syscall to our source code?

Every solution or suggestion is welcome.

Thanks in advance.
Best Regards,

			Giulio Destri
			Paolo Marenzoni
-- 

+------------------------------------+----------------------------------------+
| Giulio Destri                    					      |
| Dipartimento di Ingegneria dell'Informazione    phone   +39 521 905708/722  |
| Universita' degli Studi di Parma                fax     +39 521 905723      |
| 43100 Parma - Italy                             E-mail  destri@ce.unipr.it  |
| 					          or      destri@cm2.unipr.it |
+------------------------------------+----------------------------------------+





