[smokeping-users] Graph scale problem
G.W. Haywood
ged at jubileegroup.co.uk
Tue Apr 29 12:46:17 CEST 2008
Hello again Tobi,
On Mon, 28 Apr 2008, G.W. Haywood wrote:
> On Sat, 26 Apr 2008, Tobias Oetiker wrote:
> > G.W. Haywood wrote:
> >
> > > http://www.jubileegroup.co.uk/JOS/misc/scales_oddity.gif
> > >
> > > Maybe graphs should default to a logarithmic scale?
> >
> > The reason the 'spike' is lower in the last 10 day graph is that a
> > single pixle there represents more data than in the higher
> > resolution graphs ... the net result is, that the spike becomes
> > lower as it gets distributed across time ...
>
> With the result that the graphs give a very misleading impression of
> the data under certain circumstances.
>
> ... you've made some changes in the latest version ... I'll have
> a look at it before commenting further.
The 'smoke' rising to the top of the graphs is an improvement. I'm
now using logarithmic graphs but I'm still having difficulties with
the scales.
http://www.jubileegroup.co.uk/JOS/misc/WRT54GS4_logarithmic_graph.gif
http://www.jubileegroup.co.uk/JOS/misc/tornado_logarithmic_graph.gif
http://www.jubileegroup.co.uk/JOS/misc/webserver_logarithmic_graph.gif
As you can see a minimum RTT on the logarithmic graphs of 100us gives
rather silly results if the typical RTT is 30us...
The range selection algorithm seems not to take (much?) into account
deviations of RTT substantially above the norm. The results resemble
a hedgehog after mowing the lawn. Possibly the graph parameters need
to be individually configurable for each (probe,target) pair. FWIW my
preference would probably be for manual configuration, at least of the
graph range limits. My logic is that a particular network path will
typically have a 'normal' performance. Large excursions from normal
will be of most interest, while smaller fluctuations will tend to be
ignored. I'm thinking that I would be quite happy with a fixed upper
bound on the logarithmic graphs of ca. one second, and a lower bound
which varies by factors of say 10e+0.5 from 10us to 100ms. Obviously
anyone making ssh connections over a satellite link would want to say
something about that. :) I'll tweak the code and see how it goes.
Having griped more than enough about relatively easily fixed things
like the graph scales I think I ought to thank you for all the hard
work you've done to make SmokePing such a tremendously useful tool!
--
73,
Ged.
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