<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
Quite some time ago, Dave Taht wondered about how one would
represent bloat-induced performance problems in a diagram, and
wondered if one could have something as simple as the "three bars"
diagram you see on cell phones.<br>
<br>
I was working on a related problem, and thought about a diagram that
looked like this (a gif, and ascii in case the gif is filtered out
by the list)<img alt="" src="cid:part1.04070506.04000601@rogers.com"
height="333" width="564"><br>
<br>
In ascii art, it might look like this:<br>
======++++++++++++<br>
- +<br>
- +<br>
- +<br>
- +<br>
In the ascii, the double line is both "good" and "bad" system
performance, and they are the same up to a load of about 8, where
the "bad" line, shown as minus signs, starts to degrade. The"good"
line, shown as plus signs, stays good until a much higher load, and
only then starts diving down...<br>
<br>
<br>
The "good" line is the performance of the system when it's feeling
well, and is operating within it's limits. Pretty much a straight
line, possibly with some noise bouncing it up and down. Way out to
the right of the figure, it reaches capacity and starts curling
downwards. The "bad" line is the system when it's artificially
degraded by bufferbloat, and performance takes a dive.<br>
<br>
This is the usual "hockey stick ("_/") diagram turned on it's head
for clarity. The X axis is load, the Y is performance, and anyone
used to diagrams where "high is good" will see this system is
suffering.<br>
<br>
I think this is a fair representation, and *visually* attractive,
but I'm actually glossing over the question of units a bit. <br>
<br>
A hockey-stick curve is response time versus load. This is
something like expected response time at the top and increasing
response time as you go *downwards*. <br>
<br>
Can anyone suggest a less arbitrary metric? The best of all
possible worlds would be a non-dimensional metric, so similar data
from both small and large systems could be compared with one
another.... Perhaps twice normal, three time normal, etc???<br>
<br>
Returning to the representation problem, I think the simplest
possible diagram would literally be three bars, with the tallest
representing the expected response time, and the others some
significant degradations from that. Two bars might be the doubling
of response time, one the tripling of it, and so on.<br>
<br>
--dave<br>
<br>
<pre class="moz-signature" cols="72">--
David Collier-Brown, | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
<a class="moz-txt-link-abbreviated" href="mailto:davecb@spamcop.net">davecb@spamcop.net</a> | -- Mark Twain
(416) 223-8968
</pre>
</body>
</html>