kernel/trace/Kconfig v3.0-rc7


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


See Documentation/trace/ftrace-design.txt


C version of recordmcount available?


Deprecated power event trace API, to be removed

Provides old power event types:
C-state/idle accounting events:
and old cpufreq accounting event:
This is for userspace compatibility
and will vanish after 5 kernel iterations,
namely 2.6.41.


Allow the use of ring_buffer_swap_cpu.
Adds a very slight overhead to tracing when enabled.



Enable the kernel tracing infrastructure.


Kernel Function Tracer

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 at 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.


Kernel Function Graph Tracer

Enable the kernel to trace a function at both its return
and its entry.
Its first purpose is to trace the duration of functions and
draw a call graph for each thread with some information like
the return value. This is done by setting the current return
address on the current task structure into a stack of calls.


Interrupts-off Latency Tracer

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

echo 0 > /sys/kernel/debug/tracing/tracing_max_latency

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


Preemption-off Latency Tracer

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

echo 0 > /sys/kernel/debug/tracing/tracing_max_latency

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


Scheduling Latency Tracer

This tracer tracks the latency of the highest priority task
to be scheduled in, starting from the point it has woken up.


Trace process context switches and events

This tracer hooks to various trace points in the kernel,
allowing the user to pick and choose which trace point they
want to trace. It also includes the sched_switch tracer plugin.


Trace syscalls

Basic tracer to catch the syscall entry and exit events.


Branch Profiling

The branch profiling is a software profiler. It will add hooks
into the C conditionals to test which path a branch takes.

The likely/unlikely profiler only looks at the conditions that
are annotated with a likely or unlikely macro.

The "all branch" profiler will profile every if-statement in the
kernel. This profiler will also enable the likely/unlikely

Either of the above profilers adds a bit of overhead to the system.
If unsure, choose "No branch profiling".


No branch profiling

No branch profiling. Branch profiling adds a bit of overhead.
Only enable it if you want to analyse the branching behavior.
Otherwise keep it disabled.


Trace likely/unlikely profiler

This tracer profiles all the the likely and unlikely macros
in the kernel. It will display the results in:


Note: this will add a significant overhead; only turn this
on if you need to profile the system's use of these macros.


Profile all if conditionals

This tracer profiles all branch conditions. Every if ()
taken in the kernel is recorded whether it hit or miss.
The results will be displayed in:


This option also enables the likely/unlikely profiler.

This configuration, when enabled, will impose a great overhead
on the system. This should only be enabled when the system
is to be analyzed in much detail.


Selected by tracers that will trace the likely and unlikely
conditions. This prevents the tracers themselves from being
profiled. Profiling the tracing infrastructure can only happen
when the likelys and unlikelys are not being traced.


Trace likely/unlikely instances

This traces the events of likely and unlikely condition
calls in the kernel.  The difference between this and the
"Trace likely/unlikely profiler" is that this is not a
histogram of the callers, but actually places the calling
events into a running trace buffer to see when and where the
events happened, as well as their results.

Say N if unsure.


Trace max stack

This special tracer records the maximum stack footprint of the
kernel and displays it in /sys/kernel/debug/tracing/stack_trace.

This tracer works by hooking into every function call that the
kernel executes, and keeping a maximum stack depth value and
stack-trace saved.  If this is configured with DYNAMIC_FTRACE
then it will not have any overhead while the stack tracer
is disabled.

To enable the stack tracer on bootup, pass in 'stacktrace'
on the kernel command line.

The stack tracer can also be enabled or disabled via the
sysctl kernel.stack_tracer_enabled

Say N if unsure.


Support for tracing block IO actions

Say Y here if you want to be able to trace the block layer actions
on a given queue. Tracing allows you to see any traffic happening
on a block device queue. For more information (and the userspace
support tools needed), fetch the blktrace tools from:


Tracing also is possible using the ftrace interface, e.g.:

echo 1 > /sys/block/sda/sda1/trace/enable
echo blk > /sys/kernel/debug/tracing/current_tracer
cat /sys/kernel/debug/tracing/trace_pipe

If unsure, say N.


Enable kprobes-based dynamic events

This allows the user to add tracing events (similar to tracepoints)
on the fly via the ftrace interface. See
Documentation/trace/kprobetrace.txt for more details.

Those events can be inserted wherever kprobes can probe, and record
various register and memory values.

This option is also required by perf-probe subcommand of perf tools.
If you want to use perf tools, this option is strongly recommended.


enable/disable ftrace tracepoints dynamically

This option will modify all the calls to ftrace dynamically
(will patch them out of the binary image and replace them
with a No-Op instruction) as they are called. A table is
created to dynamically enable them again.

This way a CONFIG_FUNCTION_TRACER 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.


Kernel function profiler

This option enables the kernel function profiler. A file is created
in debugfs called function_profile_enabled which defaults to zero.
When a 1 is echoed into this file profiling begins, and when a
zero is entered, profiling stops. A "functions" file is created in
the trace_stats directory; this file shows the list of functions that
have been hit and their counters.

If in doubt, say N.


Perform a startup test on ftrace

This option performs a series of startup tests on ftrace. On bootup
a series of tests are made to verify that the tracer is
functioning properly. It will do tests on all the configured
tracers of ftrace.


Run selftest on syscall events

This option will also enable testing every syscall event.
It only enables the event and disables it and runs various loads
with the event enabled. This adds a bit more time for kernel boot
up since it runs this on every system call defined.

TBD - enable a way to actually call the syscalls as we test their


Memory mapped IO tracing

Mmiotrace traces Memory Mapped I/O access and is meant for
debugging and reverse engineering. It is called from the ioremap
implementation and works via page faults. Tracing is disabled by
default and can be enabled at run-time.

See Documentation/trace/mmiotrace.txt.
If you are not helping to develop drivers, say N.


Test module for mmiotrace

This is a dumb module for testing mmiotrace. It is very dangerous
as it will write garbage to IO memory starting at a given address.
However, it should be safe to use on e.g. unused portion of VRAM.

Say N, unless you absolutely know what you are doing.


Ring buffer benchmark stress tester

This option creates a test to stress the ring buffer and benchmark it.
It creates its own ring buffer such that it will not interfere with
any other users of the ring buffer (such as ftrace). It then creates
a producer and consumer that will run for 10 seconds and sleep for
10 seconds. Each interval it will print out the number of events
it recorded and give a rough estimate of how long each iteration took.

It does not disable interrupts or raise its priority, so it may be
affected by processes that are running.

If unsure, say N.