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From: Makey@LOGICON.ARPA (Jeff Makey)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: interrupt-driven vs. polled I/O performance
Message-ID: <416@logicon.arpa>
Date: 14 Apr 89 21:58:14 GMT
References: <14-Apr-89.114221@192.41.214.2>
Organization: Logicon, Inc., San Diego, CA
Lines: 19

In article <14-Apr-89.114221@192.41.214.2> amanda@lts.UUCP writes:
>When I first saw the code to the UNIX tty
>handler, my first question was "why are they doing all of this at
>interrupt time?"  So far, I've never seen an answer to that besides
>"historical reasons."

The reason "all of this" gets done at interrupt time is performance,
although not the kind that has been discussed so far.  In this case,
UNIX software is responsible for echoing characters, and to keep echo
delay to a minimum the character(s) actually echoed are put on the
output queue at interrupt time.  Anyone who has used TELNET (hah!
there's the relevance to TCP/IP) over a slow connection knows how
annoying delayed echo is.

                           :: Jeff Makey

Department of Tautological Pleonasms and Superfluous Redundancies Department
    Disclaimer: Logicon doesn't even know we're running news.
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