Kernel Instrumentation
Here is a listing of some instrumentation systems for the kernel:
Contents
Existing Instrumentation Systems
TimePegs
Andrew Morton's system for measuring intervals between kernel events:
See http://www.zipworld.com.au/~akpm/linux/timepeg.txt
Patches at:
http://www.zip.com.au/~akpm/linux/index.html#timepegs
Printk Times
Produces printk's with extra time data on them.
This is a very simple patch, which works for bootup time measurements, or other places where you can just jam in a printk or two.
See Printk Times
Kernel Function Instrumentation (KFI)
A system which uses a compiler flag to instrument most of the functions in the kernel. Timing data is recorded at each function entry and exit. The data can be extracted and displayed later with a command-line program.
The kernel portion of this is available in the CELF tree now.
Grep for CONFIG_KFI.
See the page Kernel Function Instrumentation page for some preliminary notes.
FIXTHIS - need to isolate this as a patch.
Linux Trace Toolkit
Kernel Tracer (in IKD patch)
This is part of a general kernel tools package, maintained by Andrea Arcangeli.
See http://www.kernel.org/pub/linux/kernel/people/andrea/ikd/README
The ktrace implementation is in the file kernel/debug/profiler.c It was originally written by Ingo Molnar, Richard Henderson and/or Andrea Arcangeli
It uses the compiler flag -pg to add profiling instrumentation to the kernel.
Function trace in KDB
Last year (Jan 2002) Jim Houston sent a patch to the kernel mailing list which provides support compiler-instrumented function calls.
See http://www.ussg.iu.edu/hypermail/linux/kernel/0201.3/0888.html
Notes
Some random thoughts on instrumentation:
- Most instrumentation systems need lots of memory to buffer the data produced
- Some instrumentation systems support filters or triggers to allow for better control over the information saved
- instrumentation systems tend to introduce overhead or otherwise interfere with the thing they are measuring
- instrumentation systems tend to pollute the cache lines for the processor
- There doesn't seem to be a single API to support in-kernel timing instrumentation which is supported on lots of different architectures. This is the main reason for CELF's current project to define an Instrumentation API
