Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!indri!ames!amdcad!rpw3
From: rpw3@amdcad.AMD.COM (Rob Warnock)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: interrupt-driven vs. polled I/O performance
Keywords: echo polling
Message-ID: <25407@amdcad.AMD.COM>
Date: 26 Apr 89 09:50:03 GMT
References: <25231@amdcad.AMD.COM> <421@logicon.arpa> <1410@xenna.Xylogics.COM>
Reply-To: rpw3@amdcad.UUCP (Rob Warnock)
Organization: [Consultant] San Mateo, CA
Lines: 36

In article <1410@xenna.Xylogics.COM> gws@Xylogics.COM (Geoff Steckel) writes:
+---------------
| There is some knowledge about human sensitivity to delays in
| tactile/aural/visual feedback...  | There are three regimes of interest:
| 0 to about 50 milliseconds: Subject doesn't notice much...
| 50 to about 500 milliseconds: The **REALLY** annoying range...
| 500 milliseconds and up:
+---------------

I completely agree with your numbers for tactile/aural [one of the
"torture tests" we applied before we'd let new announcers work at a
certain campus radio station (c.1965) was to delay the sound in their
monitor earphone from their voice by about 1/2 second -- *killer!*],
but I just can't agree in the case of visual echo to keyboarded data.
It's my experience that the second regime ("really annoying") begins
well above the 200ms range for the keyboard/display situation.

For example, I am typing this message into "vi" via a Telebit modem.
The Telebit, in "micropacket" mode, has a round-trip time of about
240ms for single-character echo (including response to cursor-motion
commands). [I just measured it.] Yet I experience no discomfort or
irritation when doing low-level editing over this modem. [Reading
news, yes, the ~1sec pause while it shifts into "long packet" mode
when displaying a new page is quite annoying. I often wish the Telebit
had something intermediate between its two modes!]

I just don't believe the thresholds are the same for all pairs of
action/perception modes, especially keyboard/display.


Rob Warnock
Systems Architecture Consultant

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