1. Dynamically Tracing
KDE
Manish Chakravarty
ThoughtWorks Studios
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2. Agenda
• Learn about DTrace
• Learn what and where to Trace
• Trace!
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3. I. What is DTrace?
While I go through the slides, please start copying the VM!
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4. DTrace is..
• a comprehensive Dynamic Tracing
framework created by Sun Microsystems
for troubleshooting kernel and application
problems in real time.
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5. Excuse me?
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6. • Dtrace enables us to “look into” the
internals of a running production application
and allows us to instrument it
• It can do very neat stuff in the kernel as
well, but that’s not the point of this session
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7. So how does DTrace
work?
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8. • Dtrace allows you to dynamically modify
the operating system kernel and user
processes to record additional data that
you specify at locations of interest, called
probes
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9. • Dtrace probes come from a set of kernel
modules called providers, each of which
performs a particular type of
instrumentation to create probes
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10. Provider:Module:Function:Name
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11. Provider
The name of the DTrace provider that is publishing this
probe
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12. Module
If this probe corresponds to a specific program
location, the name of the module which the probe is
located
The name is either the name of a kernel module or a
user library
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13. Function
If this probe corresponds to a specific program
location, the name of the program function in which the
probe is located
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14. Name
The final component of the probe name is a name that
gives you some idea of the probe’s semantic meaning
such as BEGIN or END
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15. Thus:
Provider:Module:Function:Name
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16. DTrace Architecture
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17. Let’s start Tracing!
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18. manish@belenix-KDE4:~/WorkOut/
DTraceTutorial$ pfexec dtrace -n BEGIN
dtrace: description 'BEGIN' matched 1 probe
CPU ID FUNCTION:NAME
0 1 :BEGIN
^C
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19. manish@belenix-KDE4:~/WorkOut/
DTraceTutorial$ pfexec dtrace -n BEGIN -n END
dtrace: description 'BEGIN' matched 1 probe
dtrace: description 'END' matched 1 probe
CPU ID FUNCTION:NAME
0 1 :BEGIN
^C
0 2 :END
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20. • The probe BEGIN fires every time you
start a new tracing request
• The probe END fires every time you exit
DTrace. In this case hitting Ctrl-C triggered
it.
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21. Hello, World!
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22. BEGIN
{
trace("hello, world");
exit(0);
}
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23. Output..
manish@belenix-KDE4:~/WorkOut/DTraceTutorial/1-
HelloWorld$ pfexec dtrace -s hello.d
dtrace: script 'hello.d' matched 1 probe
CPU ID FUNCTION:NAME
0 1 :BEGIN hello, world
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24. 61,809
DTrace probes on the system!
pfexec dtrace -l | wc -l
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25. DTrace Architecture
Source: http://wikis.sun.com/download/attachments/10390716/architecture.gif
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26. II. What / Where / How
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27. • Navigate to the directory having the Qt
source code
• Find out a good place in QObject to put
one
• Start writing probes!
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28. Hack!
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