kernel/trace/Kconfig

#
# Architectures that offer an FTRACE implementation should select HAVE_FTRACE:
#
config HAVE_FTRACE
	bool

config TRACER_MAX_TRACE
	bool

config TRACING
	bool
	select DEBUG_FS

config FTRACE
	bool "Kernel Function Tracer"
	depends on DEBUG_KERNEL && HAVE_FTRACE
	select FRAME_POINTER
	select TRACING
	select CONTEXT_SWITCH_TRACER
	help
	  Enable the kernel to trace every kernel function. This is done
	  by using a compiler feature to insert a small, 5-byte No-Operation
	  instruction to the beginning of every kernel function, which NOP
	  sequence is then dynamically patched into a tracer call when
	  tracing is enabled by the administrator. If it's runtime disabled
	  (the bootup default), then the overhead of the instructions is very
	  small and not measurable even in micro-benchmarks.

config IRQSOFF_TRACER
	bool "Interrupts-off Latency Tracer"
	default n
	depends on TRACE_IRQFLAGS_SUPPORT
	depends on GENERIC_TIME
	select TRACE_IRQFLAGS
	select TRACING
	select TRACER_MAX_TRACE
	help
	  This option measures the time spent in irqs-off critical
	  sections, with microsecond accuracy.

	  The default measurement method is a maximum search, which is
	  disabled by default and can be runtime (re-)started
	  via:

	      echo 0 > /debugfs/tracing/tracing_max_latency

	  (Note that kernel size and overhead increases with this option
	  enabled. This option and the preempt-off timing option can be
	  used together or separately.)

config PREEMPT_TRACER
	bool "Preemption-off Latency Tracer"
	default n
	depends on GENERIC_TIME
	depends on PREEMPT
	select TRACING
	select TRACER_MAX_TRACE
	help
	  This option measures the time spent in preemption off critical
	  sections, with microsecond accuracy.

	  The default measurement method is a maximum search, which is
	  disabled by default and can be runtime (re-)started
	  via:

	      echo 0 > /debugfs/tracing/tracing_max_latency

	  (Note that kernel size and overhead increases with this option
	  enabled. This option and the irqs-off timing option can be
	  used together or separately.)

config SCHED_TRACER
	bool "Scheduling Latency Tracer"
	depends on DEBUG_KERNEL
	select TRACING
	select CONTEXT_SWITCH_TRACER
	select TRACER_MAX_TRACE
	help
	  This tracer tracks the latency of the highest priority task
	  to be scheduled in, starting from the point it has woken up.

config CONTEXT_SWITCH_TRACER
	bool "Trace process context switches"
	depends on DEBUG_KERNEL
	select TRACING
	select MARKERS
	help
	  This tracer gets called from the context switch and records
	  all switching of tasks.

config DYNAMIC_FTRACE
	bool "enable/disable ftrace tracepoints dynamically"
	depends on FTRACE
	default y
	help
         This option will modify all the calls to ftrace dynamically
	 (will patch them out of the binary image and replaces them
	 with a No-Op instruction) as they are called. A table is
	 created to dynamically enable them again.

	 This way a CONFIG_FTRACE kernel is slightly larger, but otherwise
	 has native performance as long as no tracing is active.

	 The changes to the code are done by a kernel thread that
	 wakes up once a second and checks to see if any ftrace calls
	 were made. If so, it runs stop_machine (stops all CPUS)
	 and modifies the code to jump over the call to ftrace.