Subject: Re: ready receive

From: L J Clarke <[email-masked]>
Date: Tue, 6 Apr 93 18:08:47 BST

Peter Rigsbee writes:

> Steve Huss-Lederman writes:
> > 
> > Ready receive is a special type of send that tells the processor that
> > an appropriate receive has already been posted for this message.  On
> > some systems this allows the sender to transmit the message without
> > having to send system request/acknowledge packets (or significantly
> > reduces the number).  This effectively raises the bandwidth that the
> > user achieves on the system.  For example, on the Intel Delta ready
> > receive (forced type) can increase the bandwidth by over 20%.
> 
> I think this is a good description of ready receive.  It matches the
> description given in each meeting.
> 
> One thing that bothers me, and that is behind the reason I vote *against*
> the feature, is that while the proponents say:
> 	"some systems [can benefit]"
> they always mention the same example -- Intel systems.  No other vendor's
> MPP or cluster system ever gets mentioned, nor any of the workstation 
> packages.

I agree with this.  

I want to make a strong proposal about the argument that a 20%
improvement on the Delta is attainable, but more precisely about the
Delta in relation to MPI. 

There is one Delta.  There will never be another (conjecture, but true). 
We should place the Delta outside the set of machines which MPI does
consider.  It is of no future importance and is of trivial importance
in the present.

This means that arguments such as

"You can't do XXX on the Delta"

are not acceptable as arguments for excluding XXX from MPI,

and that arguments such as

"XXX goes ? faster than YYY on the Delta"

is not acceptable as an argument for including XXX in MPI.

> I'll start.  I do not anticipate that ready receive will be of benefit to 
> the CRAY T3D (MPP system).

I encourage vendors to add their statements.

Best Wishes
Lyndon

         /--------------------------------------------------------\
    e||) | Lyndon J Clarke    Edinburgh Parallel Computing Centre | e||) 
    c||c | Tel: 031 650 5021  Email: [email-masked]  | c||c 
         \--------------------------------------------------------/

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From: [email-masked] (Dan Nessett)
Date: Wed, 7 Apr 1993 08:32:56 -0800

For those interested in understanding the reasoning behind ready receive
and regular receive, note that the problems they solve were addressed over
20 years ago in a paper by David Walden in the April 1972 issue of CACM
(pp. 221-230). This paper discusses (among other things) the notion of a
rendezvous site for interprocess communication. Section 3 of the paper
contains the relevant information.

Dan