June 2017
Intermediate to advanced
478 pages
13h 14m
English
Enabling CONFIG_DYNAMIC_FTRACE allows Ftrace to modify the function trace sites at runtime, which has a couple of benefits. Firstly, it triggers additional build-time processing of the trace function probes, which allows the Ftrace subsystem to locate them at boot time and overwrite them with NOP instructions, thus reducing the overhead of the function trace code to almost nothing. You can then enable Ftrace in production or near-production kernels with no impact on performance.
The second advantage is that you can selectively enable function trace sites rather than tracing everything. The list of functions is put into available_filter_functions; there are several tens of thousands of them. You can selectively ...
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