linux/kernel/trace/Kconfig
Steven Rostedt 7a8e76a382 tracing: unified trace buffer
This is a unified tracing buffer that implements a ring buffer that
hopefully everyone will eventually be able to use.

The events recorded into the buffer have the following structure:

  struct ring_buffer_event {
	u32 type:2, len:3, time_delta:27;
	u32 array[];
  };

The minimum size of an event is 8 bytes. All events are 4 byte
aligned inside the buffer.

There are 4 types (all internal use for the ring buffer, only
the data type is exported to the interface users).

 RINGBUF_TYPE_PADDING: this type is used to note extra space at the end
	of a buffer page.

 RINGBUF_TYPE_TIME_EXTENT: This type is used when the time between events
	is greater than the 27 bit delta can hold. We add another
	32 bits, and record that in its own event (8 byte size).

 RINGBUF_TYPE_TIME_STAMP: (Not implemented yet). This will hold data to
	help keep the buffer timestamps in sync.

RINGBUF_TYPE_DATA: The event actually holds user data.

The "len" field is only three bits. Since the data must be
4 byte aligned, this field is shifted left by 2, giving a
max length of 28 bytes. If the data load is greater than 28
bytes, the first array field holds the full length of the
data load and the len field is set to zero.

Example, data size of 7 bytes:

	type = RINGBUF_TYPE_DATA
	len = 2
	time_delta: <time-stamp> - <prev_event-time-stamp>
	array[0..1]: <7 bytes of data> <1 byte empty>

This event is saved in 12 bytes of the buffer.

An event with 82 bytes of data:

	type = RINGBUF_TYPE_DATA
	len = 0
	time_delta: <time-stamp> - <prev_event-time-stamp>
	array[0]: 84 (Note the alignment)
	array[1..14]: <82 bytes of data> <2 bytes empty>

The above event is saved in 92 bytes (if my math is correct).
82 bytes of data, 2 bytes empty, 4 byte header, 4 byte length.

Do not reference the above event struct directly. Use the following
functions to gain access to the event table, since the
ring_buffer_event structure may change in the future.

ring_buffer_event_length(event): get the length of the event.
	This is the size of the memory used to record this
	event, and not the size of the data pay load.

ring_buffer_time_delta(event): get the time delta of the event
	This returns the delta time stamp since the last event.
	Note: Even though this is in the header, there should
		be no reason to access this directly, accept
		for debugging.

ring_buffer_event_data(event): get the data from the event
	This is the function to use to get the actual data
	from the event. Note, it is only a pointer to the
	data inside the buffer. This data must be copied to
	another location otherwise you risk it being written
	over in the buffer.

ring_buffer_lock: A way to lock the entire buffer.
ring_buffer_unlock: unlock the buffer.

ring_buffer_alloc: create a new ring buffer. Can choose between
	overwrite or consumer/producer mode. Overwrite will
	overwrite old data, where as consumer producer will
	throw away new data if the consumer catches up with the
	producer.  The consumer/producer is the default.

ring_buffer_free: free the ring buffer.

ring_buffer_resize: resize the buffer. Changes the size of each cpu
	buffer. Note, it is up to the caller to provide that
	the buffer is not being used while this is happening.
	This requirement may go away but do not count on it.

ring_buffer_lock_reserve: locks the ring buffer and allocates an
	entry on the buffer to write to.
ring_buffer_unlock_commit: unlocks the ring buffer and commits it to
	the buffer.

ring_buffer_write: writes some data into the ring buffer.

ring_buffer_peek: Look at a next item in the cpu buffer.
ring_buffer_consume: get the next item in the cpu buffer and
	consume it. That is, this function increments the head
	pointer.

ring_buffer_read_start: Start an iterator of a cpu buffer.
	For now, this disables the cpu buffer, until you issue
	a finish. This is just because we do not want the iterator
	to be overwritten. This restriction may change in the future.
	But note, this is used for static reading of a buffer which
	is usually done "after" a trace. Live readings would want
	to use the ring_buffer_consume above, which will not
	disable the ring buffer.

ring_buffer_read_finish: Finishes the read iterator and reenables
	the ring buffer.

ring_buffer_iter_peek: Look at the next item in the cpu iterator.
ring_buffer_read: Read the iterator and increment it.
ring_buffer_iter_reset: Reset the iterator to point to the beginning
	of the cpu buffer.
ring_buffer_iter_empty: Returns true if the iterator is at the end
	of the cpu buffer.

ring_buffer_size: returns the size in bytes of each cpu buffer.
	Note, the real size is this times the number of CPUs.

ring_buffer_reset_cpu: Sets the cpu buffer to empty
ring_buffer_reset: sets all cpu buffers to empty

ring_buffer_swap_cpu: swaps a cpu buffer from one buffer with a
	cpu buffer of another buffer. This is handy when you
	want to take a snap shot of a running trace on just one
	cpu. Having a backup buffer, to swap with facilitates this.
	Ftrace max latencies use this.

ring_buffer_empty: Returns true if the ring buffer is empty.
ring_buffer_empty_cpu: Returns true if the cpu buffer is empty.

ring_buffer_record_disable: disable all cpu buffers (read only)
ring_buffer_record_disable_cpu: disable a single cpu buffer (read only)
ring_buffer_record_enable: enable all cpu buffers.
ring_buffer_record_enabl_cpu: enable a single cpu buffer.

ring_buffer_entries: The number of entries in a ring buffer.
ring_buffer_overruns: The number of entries removed due to writing wrap.

ring_buffer_time_stamp: Get the time stamp used by the ring buffer
ring_buffer_normalize_time_stamp: normalize the ring buffer time stamp
	into nanosecs.

I still need to implement the GTOD feature. But we need support from
the cpu frequency infrastructure.  But this can be done at a later
time without affecting the ring buffer interface.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14 10:38:54 +02:00

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#
# Architectures that offer an FTRACE implementation should select HAVE_FTRACE:
#
config NOP_TRACER
bool
config HAVE_FTRACE
bool
select NOP_TRACER
config HAVE_DYNAMIC_FTRACE
bool
config HAVE_FTRACE_MCOUNT_RECORD
bool
config TRACER_MAX_TRACE
bool
config RING_BUFFER
bool
config TRACING
bool
select DEBUG_FS
select RING_BUFFER
select STACKTRACE
select TRACEPOINTS
config FTRACE
bool "Kernel Function Tracer"
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
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
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
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
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
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 SYSPROF_TRACER
bool "Sysprof Tracer"
depends on X86
select TRACING
help
This tracer provides the trace needed by the 'Sysprof' userspace
tool.
config SCHED_TRACER
bool "Scheduling Latency Tracer"
depends on HAVE_FTRACE
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 HAVE_FTRACE
depends on DEBUG_KERNEL
select TRACING
select MARKERS
help
This tracer gets called from the context switch and records
all switching of tasks.
config BOOT_TRACER
bool "Trace boot initcalls"
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
select TRACING
help
This tracer helps developers to optimize boot times: it records
the timings of the initcalls. Its aim is to be parsed by the
/scripts/bootgraph.pl tool to produce pretty graphics about
boot inefficiencies, giving a visual representation of the
delays during initcalls. Note that tracers self tests can't
be enabled if this tracer is selected since only one tracer
should touch the tracing buffer at a time.
config STACK_TRACER
bool "Trace max stack"
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
select FTRACE
select STACKTRACE
help
This tracer records the max stack of the kernel, and displays
it in debugfs/tracing/stack_trace
config DYNAMIC_FTRACE
bool "enable/disable ftrace tracepoints dynamically"
depends on FTRACE
depends on HAVE_DYNAMIC_FTRACE
depends on DEBUG_KERNEL
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.
config FTRACE_MCOUNT_RECORD
def_bool y
depends on DYNAMIC_FTRACE
depends on HAVE_FTRACE_MCOUNT_RECORD
config FTRACE_SELFTEST
bool
config FTRACE_STARTUP_TEST
bool "Perform a startup test on ftrace"
depends on TRACING && DEBUG_KERNEL && !BOOT_TRACER
select FTRACE_SELFTEST
help
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.