Newsgroups: comp.parallel.pvm
From: maillet@imag.fr (Eric Maillet )
Subject: [Q] Actual arrival date of a message
Organization: Institut Imag, Grenoble, France
Date: 27 Jun 1995 14:17:03 GMT
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Message-ID: <3sp3sv$od5@cosmos.imag.fr>

Hi,

for my performance experiments on my PVM applications I am interested
in the *actual date* of a message arrival, i.e. the soonest possible
instant at which a task can extract that message from PVM's system.
Thus, if a message arrived before a task calls pvm_recv, I know about
the time that message has spent in system buffers before it is extracted
by the pvm_recv operation.

Apart from periodically pvm_probe'ing or pvm_nrecv'ing for a message,
which induces considerable overhead, I see no way in PVM to know
about the actual arrival date of a message. 

A possible solution, at PVM kernel level, would be to provide the actual
arrival date of a message via a special function, say pvm_getrecvdate,
which operates on recv buffers. For example:


   struct timeval tv;

   rbuf=pvm_recv(-1,-1);
   pvm_getrecvdate(rbuf,&tv); /* get actual system reception date in tv */


Thus, if tv1 is the date when pvm_recv is called, and tv2 the date when
pvm_recv finishes

 * tv<tv1 => "tv1-tv" represents the time delay the message spent in PVM's
             system buffers. This is an important performance index. 

 * tv>tv1 => "tv-tv1" represents the delay the calling task was idle
             waiting for message arrival,
             "tv2-tv" represents the time to copy the message into the
             active receive buffer. These are also interesting performance
             indices.

What do you think about this ? Any other suggestions ?

Eric

-- 
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Eric MAILLET                                            LGI/LMC (INPG)
e-mail : Eric.Maillet@imag.fr              o            46, av. Felix Viallet
NeXT   : maillet@petole.imag.fr         --#>            F-38031 GRENOBLE CEDEX
voice  : (033) 76 57 48 73             ___>____,        FRANCE
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