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Software-based Function Profiler

This documentation introduces a software-based profiler with serial log communication. Further information about other profiling techniques are summarized in profiler_techniques.md

Time Source

In order to measure elipsed time of a function, a source of time is required. Following might be possible:

  1. RTC

  2. Trace::timestamp() method Following should be supported, but the qemu instances hangs up, when it is used:

    #include <trace/timestamp=.h>
Trace::timestamp= now  = Trace::timestamp=();

  3. Timer_session_component::now_us() This is the used time source by the Profiler

Implementation

Creating profiler log

The profiling functionality is implemented in class Profiler (include/rtcr/util/profiler.h). It depends on a Genode::Timer session. Therefore several adjustments are done in checkpointer.h, rtcr_restore_child/main.cc in order to passthrough the timer session to the profiler class.

In order to profile a function, add PROFILE_FUNCTION(_timer) to the top of your target function. A object of Profiler is created and the elapsed time of the timer session is stored. When the scope of the object ends (in this case, the function scope), ~Profiler is called. The time is measured another time and both timestamps are printed to the serial log:

\STATS\{"name": "Genode::List<Rtcr::Kcap_badge_info> Rtcr::Checkpointer::_create_kcap_mappings()", "start": 3932000, "stop": 3941000}\STATE\

Every profile log starts with \STATS\ and ends with \STATE\. It includes a json string with following attributes: name, start and stop.