From: nmm1@cus.cam.ac.uk (Nick Maclaren)
Subject: Re: Blinking Cursor in Xterm???
Nntp-Posting-Host: bootes.cus.cam.ac.uk
Organization: U of Cambridge, England
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In article <1tbpi9INNfp3@early-bird.think.com> barmar@think.com (Barry Margolin) writes:
>In article <1993May18.130845.6859@taylor.uucp> mark@taylor.uucp (Mark A. Davis) writes:
>>You are stuck in a distributed system feedback loop!  What if you are on an
>>Xterminal or running xterm over the net to another machine?  That is when the
>>load problems occur.  If you had a machine with 20 Xterminals attached and
>>they all had blinking cursors in xterm's, this could represent a considerable
>>ethernet bandwidth waste.
>
>Ethernet certainly has enough bandwidth for a few blinking cursors.  My
>Lisp Machine blinks the cursor twice a second and updates the time in the
>status line every second.  This uses under 1K bytes/second, or about .1% of
>the bandwidth of Ethernet.  A hundred of them on a single ethernet might be
>a problem, but a couple dozen should be fine.

Bandwidth is unlikely to be the problem, except over a wet string network.
One of major flaws of X is the horrendous number of transactions (and
hence process switches) that it forces upon a host.  Actual measurements
(hourly average) are 5 per second per logged in user, which can lead to
20-50 or more process switches (depending on whether each event is
filtered by the window manager as well as the applications and how
many processes are needed for each character.)

While a blinking cursor needs only the application and the networking
process, and does not add any transactions, it will add something like
10 process switches per second per user.  This is a significant increase
in overhead, especially as the application may have quite a large working
set.  If you want a rapidly blinking cursor, there could be as many
as 50.

If you want to go there, I wouldn't start from here!


Nick Maclaren
University of Cambridge Computer Laboratory,
New Museums Site, Pembroke Street,
Cambridge CB2 3QG, England.
Email:  nmm1@cus.cam.ac.uk
Tel.:   +44 223 334761
Fax:    +44 223 334679
