From: lusk@donner.mcs.anl.gov (Rusty Lusk)
Newsgroups: comp.parallel.mpi
Subject: Re: WMPI (p4 transport) process consume CPU when waiting ... how
    to wait passively?
Date: 11 Dec 1998 14:58:39 GMT
Organization: Argonne National Laboratory
Message-Id: <74rbv0$388@milo.mcs.anl.gov>
References: <74ohp1$g5n2@puligny.idt.cdc.fr> <74p58c$781@news1.newsguy.com>


In article <74p58c$781@news1.newsguy.com>, lindahl@cs.virginia.edu (Greg Lindahl) writes:
|> 
|> The ch_p4 device on Unix also does a polling loop, and will happily
|> consume all your CPU even when nothing is going on.
|> 

This is true when the ch_p4 device is configured with -comm=shared, to allow
both shared-memory and socket communication, in which case the polling loop
is switching back and forth from checking the shared-memory queues and 
checking the sockets (with a short-timeout select).  One can envision
more sophisticated schemes, but they are not implemented yet.  If one does
not configure with -comm=shared, then select is used to wait for the arrival
of a message, and no CPU is consumed.

Rusty Lusk