Newsgroups: comp.parallel.pvm
From: manchek@rudolph.cs.utk.edu (Bob Manchek)
Subject: Re: HELP understanding connection
Organization: Computer Science Dept, University of Tennessee, Knoxville
Date: 18 Jan 1996 16:46:11 GMT
Message-ID: <4dltgjINNmk4@CS.UTK.EDU>

In article <4dcv3r$gmn@link.rz.tu-ilmenau.de>, gero@thor.e-technik.tu-ilmenau.de (Gero Maeder) writes:

|> when I have a pvm application that
|> operates with group functions, how is the communication
|> done?
|> 
|> 
|> Example: I have a pvm-bcast and 7 hosts.
|> 
|> Does the group-root sends to all hosts serial
|> 1-2 1-3 1-4 1-5 1-6 1-7
|> 
|> or is it in a tree structure
|> 
|> 1-2 2-3 2-4 4-5 4-6 3-7
|> so that some communication can be done ''parallel''? (4-5 and 3-7)
|> 
|> How is this done in pvm-mcast and pvm-barrier?

Hi,

pvm_mcast takes the message from the sending task to its pvmd.  The
message is sent directly from the source pvmd to any target pvmds
(that own recipient tasks).  This is done in parallel, but since
there is usually just one bus (Ethernet) between machines, it will
take something like Nhosts times longer than a single message.
Once the message arrives at the target pvmds, it is sent to any
tasks running there (this part is in parallel because they are on
separate machines).

pvm_bcast uses pvm_mcast, after a message exchange with the group server
to get the list of recipients, so the operation is similar.

The barrier is done with a message round-trip (request / reply) from
each task to the group-server task.

Hope this helps,
b

-- 
/ Robert Manchek                University of Tennessee     /
/                               Computer Science Department /
/ (423)974-8295 / fax -8296     Ayres Hall #104             /
/ manchek@CS.UTK.EDU.           Knoxville TN  37996-1301    /
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