DTrace & Python

An introduction to DTrace and to using DTrace to inspect Python programs.

Transcript

1. DTrace & Python Conor McDermottroe @IRLConor
2. WARNING • I’ve only been using DTrace for a couple of months • Sometimes it helps to know C • Sometimes it helps to know AWK
3. What is it? • It’s like having logging everywhere • ... but without being slow • ... and with good query tools
4. What is it not? • A debugger • A profiler • A logging framework
5. How do you get it? • Solaris (>= 10) • Mac OS X (>= 10.5) • FreeBSD (>= 7.1) • Linux - https://github.com/dtrace4linux/linux
6. How do you use it? # dtrace -n '<some D>' -c /some/cmd # dtrace -s myscript.d -c /some/cmd # dtrace -s myscript.d -p 1234 # dtrace -s myscript.d
7. D Syntax provider:module:function:name /predicate goes here/ { /* body goes here */ }
8. Trace all system calls syscall:::entry { printf("%s\n", probefunc); }
9. Trace opening files syscall::open:entry { printf("%s\n", copyinstr(arg0)); }
10. Who opened /etc/passwd? syscall::open:entry /copyinstr(arg0) == "/etc/passwd"/ { printf("%s\n", execname); ustack(); }
11. What’s sending TCP traffic? tcp::tcp_output:send { printf( "%s -> %s\n", execname, args[2]->ip_daddr ); }
12. Lots of functions copyin copyinstr stringof trace tracemem printf printa count sum avg stack ustack clear trunc min max quantize stop copyout copyoutstr breakpoint panic chill
13. What about Python? • You need a patched copy of Python • Already patched on Solaris • OS X: brew install python --with-dtrace • WARNING: The syntax may differ, depending on the patch
14. Trace Python function calls :Python::function-entry { printf( "%s:%d %s", copyinstr(arg0), arg2, copyinstr(arg1) ); }
15. Timing breakdown for sub :Python::function-entry /copyinstr(arg1) == "sub"/ { self->start = timestamp; } :Python::function-return /copyinstr(arg1) == "sub"/ { self->t = timestamp - self->start; @time[execname] = quantize(self->t); self->ts = 0; }
16. Timing breakdown for sub Python value ------------- Distribution ------------- count 65536 | 0 131072 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 7 262144 |@@@@@ 1 524288 | 0
17. Trace Python function calls :Python::function-entry /copyinstr(arg1) == "sub"/ { ustack(); }
18. Trace Python object creation :Python::instance-new-start { self->classname = copyinstr(arg0); printf("%s\n", self->classname); }
19. Things to look out for • It’s fast but it's not free - be selective • Probe names may differ across operating systems • For non-standard probes arg documentation can be sparse
20. Links • http://docs.oracle.com/cd/E18752_01/pdf/819-5488.pdf • http://www.brendangregg.com/dtrace.html#DTraceToolkit • http://bugs.python.org/issue13405 • https://blogs.oracle.com/brendan/resource/DTrace-cheatsheet.pdf
21. QUESTIONS