Commit 4a88d44a authored by Albin Tonnerre's avatar Albin Tonnerre Committed by Frederic Weisbecker
Browse files

tracing: Remove mentioning of legacy latency_trace file from documentation 



The latency_trace file got removed a while back by commit
886b5b73 and has been replaced
by the latency-format option.

This patch fixes the documentation by reflecting this change.

Changes since v1:
 - mention that the trace format is configurable through the
   latency-format option
 - Fix a couple mistakes related to the timestamps

Signed-off-by: default avatarAlbin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20090831204007.GE4237@pc-ras4041.res.insa>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent c58b4321

Documentation/trace/ftrace.txt

+36 −32
Original line number Diff line number Diff line
@@ -85,26 +85,19 @@ of ftrace. Here is a list of some of the key files: 
	This file holds the output of the trace in a human

	readable format (described below).



  latency_trace:



	This file shows the same trace but the information

	is organized more to display possible latencies

	in the system (described below).



  trace_pipe:



	The output is the same as the "trace" file but this

	file is meant to be streamed with live tracing.

	Reads from this file will block until new data

	is retrieved. Unlike the "trace" and "latency_trace"

	files, this file is a consumer. This means reading

	from this file causes sequential reads to display

	more current data. Once data is read from this

	file, it is consumed, and will not be read

	again with a sequential read. The "trace" and

	"latency_trace" files are static, and if the

	tracer is not adding more data, they will display

	the same information every time they are read.

	Reads from this file will block until new data is

	retrieved.  Unlike the "trace" file, this file is a

	consumer. This means reading from this file causes

	sequential reads to display more current data. Once

	data is read from this file, it is consumed, and

	will not be read again with a sequential read. The

	"trace" file is static, and if the tracer is not

	adding more data,they will display the same

	information every time they are read.



  trace_options:
@@ -117,10 +110,10 @@ of ftrace. Here is a list of some of the key files: 
	Some of the tracers record the max latency.

	For example, the time interrupts are disabled.

	This time is saved in this file. The max trace

	will also be stored, and displayed by either

	"trace" or "latency_trace".  A new max trace will

	only be recorded if the latency is greater than

	the value in this file. (in microseconds)

	will also be stored, and displayed by "trace".

	A new max trace will only be recorded if the

	latency is greater than the value in this

	file. (in microseconds)



  buffer_size_kb:
@@ -210,7 +203,7 @@ Here is the list of current tracers that may be configured. 
	the trace with the longest max latency.

	See tracing_max_latency. When a new max is recorded,

	it replaces the old trace. It is best to view this

	trace via the latency_trace file.

	trace with the latency-format option enabled.



  "preemptoff"
@@ -307,8 +300,8 @@ the lowest priority thread (pid 0). 
Latency trace format

--------------------



For traces that display latency times, the latency_trace file

gives somewhat more information to see why a latency happened.

When the latency-format option is enabled, the trace file gives

somewhat more information to see why a latency happened.

Here is a typical trace.



# tracer: irqsoff
@@ -380,9 +373,10 @@ explains which is which. 


The above is mostly meaningful for kernel developers.



  time: This differs from the trace file output. The trace file output

	includes an absolute timestamp. The timestamp used by the

	latency_trace file is relative to the start of the trace.

  time: When the latency-format option is enabled, the trace file

	output includes a timestamp relative to the start of the

	trace. This differs from the output when latency-format

	is disabled, which includes an absolute timestamp.



  delay: This is just to help catch your eye a bit better. And

	 needs to be fixed to be only relative to the same CPU.
@@ -440,7 +434,8 @@ Here are the available options: 
  sym-addr:

   bash-4000  [01]  1477.606694: simple_strtoul <c0339346>



  verbose - This deals with the latency_trace file.

  verbose - This deals with the trace file when the

            latency-format option is enabled.



    bash  4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \

    (+0.000ms): simple_strtoul (strict_strtoul)
@@ -472,7 +467,7 @@ Here are the available options: 
		the app is no longer running



		The lookup is performed when you read

		trace,trace_pipe,latency_trace. Example:

		trace,trace_pipe. Example:



		a.out-1623  [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0

x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
@@ -481,6 +476,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] 
	       every scheduling event. Will add overhead if

	       there's a lot of tasks running at once.



  latency-format - This option changes the trace. When

                   it is enabled, the trace displays

                   additional information about the

                   latencies, as described in "Latency

                   trace format".



sched_switch

------------
@@ -596,12 +596,13 @@ To reset the maximum, echo 0 into tracing_max_latency. Here is 
an example:



 # echo irqsoff > current_tracer

 # echo latency-format > trace_options

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > tracing_enabled

 # cat latency_trace

 # cat trace

# tracer: irqsoff

#

irqsoff latency trace v1.1.5 on 2.6.26
@@ -703,12 +704,13 @@ which preemption was disabled. The control of preemptoff tracer 
is much like the irqsoff tracer.



 # echo preemptoff > current_tracer

 # echo latency-format > trace_options

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > tracing_enabled

 # cat latency_trace

 # cat trace

# tracer: preemptoff

#

preemptoff latency trace v1.1.5 on 2.6.26-rc8
@@ -850,12 +852,13 @@ Again, using this trace is much like the irqsoff and preemptoff 
tracers.



 # echo preemptirqsoff > current_tracer

 # echo latency-format > trace_options

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > tracing_enabled

 # cat latency_trace

 # cat trace

# tracer: preemptirqsoff

#

preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
@@ -1012,11 +1015,12 @@ Instead of performing an 'ls', we will run 'sleep 1' under 
'chrt' which changes the priority of the task.



 # echo wakeup > current_tracer

 # echo latency-format > trace_options

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # chrt -f 5 sleep 1

 # echo 0 > tracing_enabled

 # cat latency_trace

 # cat trace

# tracer: wakeup

#

wakeup latency trace v1.1.5 on 2.6.26-rc8

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