HP Caliper Ktrace Features Guide

Figure 1-1 Trace Buffers
Trace Points
A trace point is a place where the kernel will branch to tracing code, collect data for a
trace record, then resume normal processing. ktracer -b (begin tracing) sets a trace
point at each selected function and begins data collection. ktracer —h halts all data
collection and removes all trace points, restoring original performance. You can
customize a set of trace points dynamically for each test you make.
Trace Buffer Management
While your application is executing and each time a specified function is encountered,
a trace record is written into a trace buffer. When the trace buffer is full, the oldest
records will be overwritten. You can avoid trace buffer overflow by doing one or more
of the following tasks:
• Increase the number of records each CPU can store (ktracer -A numtraces).
• Limit the list of functions to trace.
• Stop tracing frequently called procedures:
Remove a specified function from the function list: ktracer -r func
Remove all functions from the function list: ktracer -z
How does Kernel Tracing Work? 15