diskstat 0.1: simple tool to study io patterns via relayfs

[bert hubert]

It is with distinct lack of pride that I release version 0.1 of diskstat
'Geeks in Black Thorn', a tool that allows you to generate the kinds of
graphs as presented in my OLS talk 'On faster application startup times:
Cache stuffing, seek profiling, adaptive preloading'. The lack of pride is
because this release is more a promise of what is to come than how things
should be.

The presentation, paper, and software can be found on
http://ds9a.nl/diskstat and
http://ds9a.nl/diskstat/diskstat-0.1.tar.gz

>From the README:
The quality of this code is abysmal, for which I squarely blame the fun
people at OLS who've been keeping me from my code!
(...)
The next version will be based on k/jprobes, and will make better use of
relayfs features. This also means you won't have to patch your kernel
anymore, as long as you compiled with kprobes support.

Sample command lines:
   # mkdir /relay
   # mount -t relayfs none /relay
   # ./dumpdiskstat /relay/diskstat0  > dump

   This will output something like:
   I think we skipped at 90867, ret=0
   I think we hit end at 143016, ret=-1
   I think we hit the break again 90867, ret=0

 Process the stats.
   $ ./dswalk < dump

   It will print out huge latencies encountered:

>  Large latency 163.352 on line 14146
   Total read started: 33888768, total ended: 33888768
   Total write started: 1372160, total ended: 1372160
   Waiting time: 10.695 seconds

 Make pretty plots
   gnuplot
   plot 'startplaces.dat', 'headplaces.dat'
   plot 'inflight.dat'

Continue reading on http://ds9a.nl/diskstat/README

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