Maverick config review: Tracers

[Chase Douglas]

As one of my work items, I was tasked with determining what tracer
configuration options should be enabled in the Maverick kernel. I
queried upstream about this and other tracer options. It seems that
tracer options fall into one of three categories:

 * Function tracing features (profiling, stack tracing, etc.)
 * Interesting features exposed through ftrace interfaces (SCHED_TRACER,
FTRACE_SYSCALLS)
 * Duplicated features (KSYM_TRACER, KMEMTRACE, BOOT_TRACE,
SYSPROF_TRACER)

The first category is really good stuff we should always have enabled
where appropriate moving forward.

It appears that stuff in the second category above move to perf tools in
the long term. However, there is no great replacement for their
functionality at this time, so it makes sense to enable them now.

My queries highlighted to others upstream that stuff in the third
category should go away. The discussion has already turned toward
removing some of these features from the kernel. Thus, I've decided to
leave them disabled in Maverick.

Turning to KSYM_TRACER specifically, it looks really cool, but I was
told that much better functionality was present in perf.

I hope that helps clear the fog around the current state of tracers in
the kernel. I am going to try to learn more about perf as it seems to be
the way forward when it comes to things outside of function tracing.

-- Chase