Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 (Fortune) 6/7/84; site dmsd.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!houxm!vax135!cornell!uw-beaver!tektronix!hplabs!hpda!dmsd!bass
From: bass@dmsd.UUCP (John Bass)
Newsgroups: net.arch
Subject: Re: dumber terminal device drivers
Message-ID: <191@dmsd.UUCP>
Date: Tue, 9-Apr-85 04:14:42 EST
Article-I.D.: dmsd.191
Posted: Tue Apr  9 04:14:42 1985
Date-Received: Thu, 11-Apr-85 00:35:45 EST
References: <327@piggy.UUCP> <2536@nsc.UUCP>, <209@osiris.UUCP> <528@hou2d.UUCP>
Lines: 41

As noted by others is that the real killer is the tty system call times --
as there are atleast TWO such calls -- one read and one write to echo the char.
The reason the echo is done in most applications is that they require sending
cursor position and control information which MUST NOT have echoed input
interleaved into it. Thus on most mini & micro unix systems this consumes
about 7-15ms per keystroke including user time, system calls, and context
switch.

In most user interfaces the REAL KILLER is that the user interface suffers
keystroke echo latencys of up to several seconds depending on the jobs
relative priority at the time and the amount of paging/swapping that occurs.
These LONG echo times occur on most machines under light load when ABUNDANT
memory is not available -- several times what is needed under a better
user interface. For most commercial systems this makes even the fastest
systems appear doggy at times when compared to dedicated micros like the
IBM PC.

The best solution for multiuser systems is to EXPAND the keyboard input
function to include a break bitmap and an echo bit map -- plus extend the
terminal interface to include a 1D line editor with left-right margin control
and max window size - this is a minor change to V7 tty routines and is
backward compatable with V7 line sematics. A Special IOCTL to tty is added
to read/write the editor params and another IOCTL to preset the cannon buffer.

The net effect is a HOT KEYBOARD user interface that is line oriented and
takes the guts of keyboard handling in most data editor user interfaced and
makes it REALTIME at the users terminal. Since the number of system calls
and context switches are reduced the system handles heavy loads better and
still provides dedicated system type response times. IT IS VERY IMPORTANT
not to get carried away with too much functionality since this MUST be done
at input interrrupt time -- you cann't afford to do a wakeup/context switch.
Several V6 exeriments in the late 70's died due to getting too fanncy -- they
tried doing complete window management at a very severe performance cost
for non-window applications.

I have code and a document presenting this approach. It comes from work done
over the last 8 years on various unix systems. I raised this issue as
an item for the /usr/group/standards committee but have sat the proposal waiting
for the IEEE change over to settle out.

John Bass