Number: 1517

Date: 27-Jun-84 13':47':48

Submitter: Sannella.PA

Source: Masinter.pa

Subject: Allow packet lookahead in DEI, Unix Leaf servers

Assigned To: 

Attn: Lisp, vanMelle

Status: Open

In/By: 

Problem Type: Performance

Impact: Serious

Difficulty: Hard

Frequency: Everytime

Priority: Unlikely

System: Communications

Subsystem: VAX Server

Machine: 1132

Disk: 

Lisp Version: 

Source Files: 

Microcode Version: 

Memory Size: 

File Server: 

Server Software Version: 

Disposition: 

Description: '
Date': 27 Jun 84 10':39 PDT'
From': masinter.pa'
Subject': [Eric Schoen <Schoen@SUMEX-AIM.ARPA>': Interlisp-D Filing]'
To': LispSupport'
cc': Sheil'
'
Please add ARs under Communication/VAX Server, priority Unlikely, Impact': Serious, Difficulty': Hard, Attn': Lisp, Subject': "Add packet buffering to DEI, Unix Leaf servers"'
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Return-Path': <SCHOEN@SUMEX-AIM.ARPA>'
Redistributed': Xerox1100UsersGroup^.PA'
Received': from SUMEX-AIM.ARPA by Xerox.ARPA ; 11 JUN 84 22':20':59 PDT'
Date': Mon, 11 Jun 84 22':14':03 PDT'
From': Eric Schoen <Schoen@SUMEX-AIM.ARPA>'
Subject': Interlisp-D Filing'
To': 1100users@SUMEX-AIM.ARPA'
'
I haven''t encountered a good system for handling multiple versions of source'
files in any language.  However, rather than light a flame on that topic, I''d'
like to address the issue of file server performance.'
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Early versions of Interlisp-D (Allegro through Chorus [Feb, 1983]) used an implementation of the Leaf protocol which used an outstanding request window of exactly 1 packet; that is, no lookahead was performed on the connection, reducing a competant virtual circuit protocol to an expensive request-response model.  I developed the Tenex/Tops-20 server under these Lisp versions.'
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Later versions of Interlisp support multiple-packet lookahead for situations in which the system detects sequential reading or writing (e.g. making or loading files).  The Tops-20 server hasn''t been updated to support multiple packet lookahead, however (well, the code''s in there, but not too well debugged under certain circumstances).  The result is dead time between  a response and the next request.'
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We recently implemented a brand-new Leaf server, written in Bliss to run under our own Pup environment on VAX/VMS.  The server supports up to 5 packet lookahead (Lisp uses only 1 packet, though).  Thus, there''s no deadtime between response and next request; the next request has already been made, and the response is (hopefully) already back at the D-machine.  I''ve measured 200KB throughput between a timeshared VAX-11/780 and our Dorado (loading .DCOM files), with a Dolphin-based 3-10 MB Interlisp gateway in the path.  On the other hand, the Tops-20 Leaf server, on a 2020 running on the same 3 MB net as the Dorado, with no users, can only push about 30 KB to the Dorado.'
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So the point of all this is that Leaf server efficiency is paramount to good file I/O in Interlisp.  I haven''t seen the latest Unix Leaf server, but the version we had at SDR did no lookahead.  We had patched that version to run under our VMS environment for a time, and saw roughly the same performance as the 2020.  Note that in a (multiple) gateway environment, packet lookahead can do quite a bit to mask gateway delays (so long as your networks are reasonably reliable).'
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Eric'
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Workaround: 

Test Case: 

Edit-By: vanMelle

Edit-Date: 14-Aug-84 12':14':48