linux-toradex.git/Documentation/trace/ftrace.txt, branch v4.1.22

Documentation: Fix the wrong command `echo -1 > set_ftrace_pid` for cleaning the filter.

2015-02-09T16:04:17+00:00

The command `echo > set_ftrace_pid` should be used to clean the filter quietly.
because the command `echo -1 >  set_ftrace_pid` will output the following:
"bash: echo: write error: Invalid argument".

so update the file Documentation/trace/ftrace.txt.

Signed-off-by: Wang Long 
Acked-by: Steven Rostedt 
Signed-off-by: Jonathan Corbet

tracing: Add additional marks to signal very large time deltas

2014-12-03T22:10:13+00:00

Currently, function graph tracer prints "!" or "+" just before
function execution time to signal a function overhead, depending
on the time. And some tracers tracing latency also print "!" or
"+" just after time to signal overhead, depending on the interval
between events. Even it is usually enough to do that, we sometimes
need to signal for bigger execution time than 100 micro seconds.

For example, I used function graph tracer to detect if there is
any case that exit_mm() takes too much time. I did following steps
in /sys/kernel/debug/tracing. It was easier to detect very large
excution time with patched kernel than with original kernel.

$ echo exit_mm > set_graph_function
$ echo function_graph > current_tracer
$ echo > trace
$ cat trace_pipe > $LOGFILE
 ... (do something and terminate logging)
$ grep "\\$" $LOGFILE
 3) $ 22082032 us |                      } /* kernel_map_pages */
 3) $ 22082040 us |                    } /* free_pages_prepare */
 3) $ 22082113 us |                  } /* free_hot_cold_page */
 3) $ 22083455 us |                } /* free_hot_cold_page_list */
 3) $ 22083895 us |              } /* release_pages */
 3) $ 22177873 us |            } /* free_pages_and_swap_cache */
 3) $ 22178929 us |          } /* unmap_single_vma */
 3) $ 22198885 us |        } /* unmap_vmas */
 3) $ 22206949 us |      } /* exit_mmap */
 3) $ 22207659 us |    } /* mmput */
 3) $ 22207793 us |  } /* exit_mm */

And then, it was easy to find out that a schedule-out occured by
sub_preempt_count() within kernel_map_pages().

To detect very large function exection time caused by either problematic
function implementation or scheduling issues, this patch can be useful.

Link: http://lkml.kernel.org/r/1416789259-24038-1-git-send-email-byungchul.park@lge.com

Signed-off-by: Byungchul Park 
Signed-off-by: Steven Rostedt

ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict

2014-11-21T19:42:10+00:00

Introduce FTRACE_OPS_FL_IPMODIFY to avoid conflict among
ftrace users who may modify regs->ip to change the execution
path. If two or more users modify the regs->ip on the same
function entry, one of them will be broken. So they must add
IPMODIFY flag and make sure that ftrace_set_filter_ip() succeeds.

Note that ftrace doesn't allow ftrace_ops which has IPMODIFY
flag to have notrace hash, and the ftrace_ops must have a
filter hash (so that the ftrace_ops can hook only specific
entries), because it strongly depends on the address and
must be allowed for only few selected functions.

Link: http://lkml.kernel.org/r/20141121102516.11844.27829.stgit@localhost.localdomain

Cc: Jiri Kosina 
Cc: Seth Jennings 
Cc: Petr Mladek 
Cc: Vojtech Pavlik 
Cc: Miroslav Benes 
Cc: Ingo Molnar 
Cc: Ananth N Mavinakayanahalli 
Cc: Josh Poimboeuf 
Cc: Namhyung Kim 
Signed-off-by: Masami Hiramatsu 
[ fixed up some of the comments ]
Signed-off-by: Steven Rostedt

sched: Transform resched_task() into resched_curr()

2014-07-16T11:38:19+00:00

We always use resched_task() with rq->curr argument.
It's not possible to reschedule any task but rq's current.

The patch introduces resched_curr(struct rq *) to
replace all of the repeating patterns. The main aim
is cleanup, but there is a little size profit too:

  (before)
	$ size kernel/sched/built-in.o
	   text	   data	    bss	    dec	    hex	filename
	155274	  16445	   7042	 178761	  2ba49	kernel/sched/built-in.o

	$ size vmlinux
	   text	   data	    bss	    dec	    hex	filename
	7411490	1178376	 991232	9581098	 92322a	vmlinux

  (after)
	$ size kernel/sched/built-in.o
	   text	   data	    bss	    dec	    hex	filename
	155130	  16445	   7042	 178617	  2b9b9	kernel/sched/built-in.o

	$ size vmlinux
	   text	   data	    bss	    dec	    hex	filename
	7411362	1178376	 991232	9580970	 9231aa	vmlinux

	I was choosing between resched_curr() and resched_rq(),
	and the first name looks better for me.

A little lie in Documentation/trace/ftrace.txt. I have not
actually collected the tracing again. With a hope the patch
won't make execution times much worse :)

Signed-off-by: Kirill Tkhai 
Signed-off-by: Peter Zijlstra 
Cc: Linus Torvalds 
Cc: Randy Dunlap 
Cc: Steven Rostedt 
Link: http://lkml.kernel.org/r/20140628200219.1778.18735.stgit@localhost
Signed-off-by: Ingo Molnar

tracing: Add funcgraph_tail option to print function name after closing braces

2014-05-21T03:29:32+00:00

In the function-graph tracer, add a funcgraph_tail option
to print the function name on all } lines, not just
functions whose first line is no longer in the trace
buffer.

If a function calls other traced functions, its total
time appears on its } line.  This change allows grep
to be used to determine the function for which the
line corresponds.

Update Documentation/trace/ftrace.txt to describe
this new option.

Link: http://lkml.kernel.org/p/20140520221041.8359.6782.stgit@beardog.cce.hp.com

Signed-off-by: Robert Elliott 
Signed-off-by: Steven Rostedt

ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED

2013-11-11T11:43:39+00:00

Since the introduction of PREEMPT_NEED_RESCHED in:

  f27dde8deef3 ("sched: Add NEED_RESCHED to the preempt_count")

we need to be able to look at both TIF_NEED_RESCHED and
PREEMPT_NEED_RESCHED to understand the full preemption behaviour.

Add it to the trace output.

Signed-off-by: Peter Zijlstra 
Acked-by: Steven Rostedt 
Cc: Fengguang Wu 
Cc: Huang Ying 
Cc: Yuanhan Liu 
Link: http://lkml.kernel.org/r/20131004152826.GP3081@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar

Documentation: replace strict_strtoul() with kstrtoul()

2013-08-20T10:56:26+00:00

The usage of strict_strtoul() is not preferred, because
strict_strtoul() is obsolete. Thus, kstrtoul() should be
used.

Signed-off-by: Jingoo Han 
Signed-off-by: Jiri Kosina

tracing: Add function probe to trigger a ftrace dump of current CPU trace

2013-06-11T22:38:48+00:00

Add the "cpudump" command to have the current CPU ftrace buffer dumped
to console if a function is hit. This is useful when debugging a
tripple fault, where you have an idea of a function that is called
just before the tripple fault occurs, and can tell ftrace to dump its
content out to the console before it continues.

This differs from the "dump" command as it only dumps the content of
the ring buffer for the currently executing CPU, and does not show
the contents of the other CPUs.

Format is:

  :cpudump

echo 'bad_address:cpudump' > /debug/tracing/set_ftrace_filter

To remove this:

echo '!bad_address:cpudump' > /debug/tracing/set_ftrace_filter

Signed-off-by: Steven Rostedt

tracing: Add function probe to trigger a ftrace dump to console

2013-06-11T22:38:46+00:00

Add the "dump" command to have the ftrace buffer dumped to console if
a function is hit. This is useful when debugging a tripple fault,
where you have an idea of a function that is called just before the
tripple fault occurs, and can tell ftrace to dump its content out
to the console before it continues.

Format is:

  :dump

echo 'bad_address:dump' > /debug/tracing/set_ftrace_filter

To remove this:

echo '!bad_address:dump' > /debug/tracing/set_ftrace_filter

Requested-by: Luis Claudio R. Goncalves 
Signed-off-by: Steven Rostedt

tracing: Bring Documentation/trace/ftrace.txt up to date

2013-03-15T04:36:10+00:00

The ftrace.txt document has been suffering from some serious bit rot.

Updated the current content to how things are as of v3.10.
Remove things that no longer exist.
Add documentation about new features:
  per_cpu
  stats
  instances
  stack trace
  etc.

Signed-off-by: Steven Rostedt