Commit 156f5a78 authored by GeunSik Lim's avatar GeunSik Lim Committed by Greg Kroah-Hartman
Browse files

debugfs: Fix terminology inconsistency of dir name to mount debugfs filesystem. 

Many developers use "/debug/" or "/debugfs/" or "/sys/kernel/debug/"
directory name to mount debugfs filesystem for ftrace according to
./Documentation/tracers/ftrace.txt file.

And, three directory names(ex:/debug/, /debugfs/, /sys/kernel/debug/) is
existed in kernel source like ftrace, DRM, Wireless, Documentation,
Network[sky2]files to mount debugfs filesystem.

debugfs means debug filesystem for debugging easy to use by greg kroah
hartman. "/sys/kernel/debug/" name is suitable as directory name
of debugfs filesystem.
- debugfs related reference: http://lwn.net/Articles/334546/



Fix inconsistency of directory name to mount debugfs filesystem.

* From Steven Rostedt
  - find_debugfs() and tracing_files() in this patch.

Signed-off-by: default avatarGeunSik Lim <geunsik.lim@samsung.com>
Acked-by     : Inaky Perez-Gonzalez <inaky@linux.intel.com>
Reviewed-by  : Steven Rostedt <rostedt@goodmis.org>
Reviewed-by  : James Smart <james.smart@emulex.com>
CC: Jiri Kosina <trivial@kernel.org>
CC: David Airlie <airlied@linux.ie>
CC: Peter Osterlund <petero2@telia.com>
CC: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
CC: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
CC: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 1b713e00

Documentation/DocBook/debugobjects.tmpl

+1 −1
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ 
      number of errors are printk'ed including a full stack trace.

    </para>

    <para>

      The statistics are available via debugfs/debug_objects/stats.

      The statistics are available via /sys/kernel/debug/debug_objects/stats.

      They provide information about the number of warnings and the

      number of successful fixups along with information about the

      usage of the internal tracking objects and the state of the

Documentation/cdrom/packet-writing.txt

+1 −1
Original line number Diff line number Diff line
@@ -117,7 +117,7 @@ Using the pktcdvd debugfs interface 


To read pktcdvd device infos in human readable form, do:



	# cat /debug/pktcdvd/pktcdvd[0-7]/info

	# cat /sys/kernel/debug/pktcdvd/pktcdvd[0-7]/info



For a description of the debugfs interface look into the file:

Documentation/fault-injection/fault-injection.txt

+35 −35
Original line number Diff line number Diff line
@@ -29,16 +29,16 @@ o debugfs entries 
fault-inject-debugfs kernel module provides some debugfs entries for runtime

configuration of fault-injection capabilities.



- /debug/fail*/probability:

- /sys/kernel/debug/fail*/probability:



	likelihood of failure injection, in percent.

	Format: <percent>



	Note that one-failure-per-hundred is a very high error rate

	for some testcases.  Consider setting probability=100 and configure

	/debug/fail*/interval for such testcases.

	/sys/kernel/debug/fail*/interval for such testcases.



- /debug/fail*/interval:

- /sys/kernel/debug/fail*/interval:



	specifies the interval between failures, for calls to

	should_fail() that pass all the other tests.
@@ -46,18 +46,18 @@ configuration of fault-injection capabilities. 
	Note that if you enable this, by setting interval>1, you will

	probably want to set probability=100.



- /debug/fail*/times:

- /sys/kernel/debug/fail*/times:



	specifies how many times failures may happen at most.

	A value of -1 means "no limit".



- /debug/fail*/space:

- /sys/kernel/debug/fail*/space:



	specifies an initial resource "budget", decremented by "size"

	on each call to should_fail(,size).  Failure injection is

	suppressed until "space" reaches zero.



- /debug/fail*/verbose

- /sys/kernel/debug/fail*/verbose



	Format: { 0 | 1 | 2 }

	specifies the verbosity of the messages when failure is
@@ -65,17 +65,17 @@ configuration of fault-injection capabilities. 
	log line per failure; '2' will print a call trace too -- useful

	to debug the problems revealed by fault injection.



- /debug/fail*/task-filter:

- /sys/kernel/debug/fail*/task-filter:



	Format: { 'Y' | 'N' }

	A value of 'N' disables filtering by process (default).

	Any positive value limits failures to only processes indicated by

	/proc/<pid>/make-it-fail==1.



- /debug/fail*/require-start:

- /debug/fail*/require-end:

- /debug/fail*/reject-start:

- /debug/fail*/reject-end:

- /sys/kernel/debug/fail*/require-start:

- /sys/kernel/debug/fail*/require-end:

- /sys/kernel/debug/fail*/reject-start:

- /sys/kernel/debug/fail*/reject-end:



	specifies the range of virtual addresses tested during

	stacktrace walking.  Failure is injected only if some caller
@@ -84,26 +84,26 @@ configuration of fault-injection capabilities. 
	Default required range is [0,ULONG_MAX) (whole of virtual address space).

	Default rejected range is [0,0).



- /debug/fail*/stacktrace-depth:

- /sys/kernel/debug/fail*/stacktrace-depth:



	specifies the maximum stacktrace depth walked during search

	for a caller within [require-start,require-end) OR

	[reject-start,reject-end).



- /debug/fail_page_alloc/ignore-gfp-highmem:

- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:



	Format: { 'Y' | 'N' }

	default is 'N', setting it to 'Y' won't inject failures into

	highmem/user allocations.



- /debug/failslab/ignore-gfp-wait:

- /debug/fail_page_alloc/ignore-gfp-wait:

- /sys/kernel/debug/failslab/ignore-gfp-wait:

- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:



	Format: { 'Y' | 'N' }

	default is 'N', setting it to 'Y' will inject failures

	only into non-sleep allocations (GFP_ATOMIC allocations).



- /debug/fail_page_alloc/min-order:

- /sys/kernel/debug/fail_page_alloc/min-order:



	specifies the minimum page allocation order to be injected

	failures.
@@ -166,13 +166,13 @@ o Inject slab allocation failures into module init/exit code 
#!/bin/bash



FAILTYPE=failslab

echo Y > /debug/$FAILTYPE/task-filter

echo 10 > /debug/$FAILTYPE/probability

echo 100 > /debug/$FAILTYPE/interval

echo -1 > /debug/$FAILTYPE/times

echo 0 > /debug/$FAILTYPE/space

echo 2 > /debug/$FAILTYPE/verbose

echo 1 > /debug/$FAILTYPE/ignore-gfp-wait

echo Y > /sys/kernel/debug/$FAILTYPE/task-filter

echo 10 > /sys/kernel/debug/$FAILTYPE/probability

echo 100 > /sys/kernel/debug/$FAILTYPE/interval

echo -1 > /sys/kernel/debug/$FAILTYPE/times

echo 0 > /sys/kernel/debug/$FAILTYPE/space

echo 2 > /sys/kernel/debug/$FAILTYPE/verbose

echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait



faulty_system()

{
@@ -217,20 +217,20 @@ then 
	exit 1

fi



cat /sys/module/$module/sections/.text > /debug/$FAILTYPE/require-start

cat /sys/module/$module/sections/.data > /debug/$FAILTYPE/require-end

cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start

cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end



echo N > /debug/$FAILTYPE/task-filter

echo 10 > /debug/$FAILTYPE/probability

echo 100 > /debug/$FAILTYPE/interval

echo -1 > /debug/$FAILTYPE/times

echo 0 > /debug/$FAILTYPE/space

echo 2 > /debug/$FAILTYPE/verbose

echo 1 > /debug/$FAILTYPE/ignore-gfp-wait

echo 1 > /debug/$FAILTYPE/ignore-gfp-highmem

echo 10 > /debug/$FAILTYPE/stacktrace-depth

echo N > /sys/kernel/debug/$FAILTYPE/task-filter

echo 10 > /sys/kernel/debug/$FAILTYPE/probability

echo 100 > /sys/kernel/debug/$FAILTYPE/interval

echo -1 > /sys/kernel/debug/$FAILTYPE/times

echo 0 > /sys/kernel/debug/$FAILTYPE/space

echo 2 > /sys/kernel/debug/$FAILTYPE/verbose

echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait

echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem

echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth



trap "echo 0 > /debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT

trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT



echo "Injecting errors into the module $module... (interrupt to stop)"

sleep 1000000

Documentation/kprobes.txt

+3 −3
Original line number Diff line number Diff line
@@ -507,9 +507,9 @@ http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115) 
Appendix A: The kprobes debugfs interface



With recent kernels (> 2.6.20) the list of registered kprobes is visible

under the /debug/kprobes/ directory (assuming debugfs is mounted at /debug).

under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at //sys/kernel/debug).



/debug/kprobes/list: Lists all registered probes on the system

/sys/kernel/debug/kprobes/list: Lists all registered probes on the system



c015d71a  k  vfs_read+0x0

c011a316  j  do_fork+0x0
@@ -525,7 +525,7 @@ virtual addresses that correspond to modules that've been unloaded), 
such probes are marked with [GONE]. If the probe is temporarily disabled,

such probes are marked with [DISABLED].



/debug/kprobes/enabled: Turn kprobes ON/OFF forcibly.

/sys/kernel/debug/kprobes/enabled: Turn kprobes ON/OFF forcibly.



Provides a knob to globally and forcibly turn registered kprobes ON or OFF.

By default, all kprobes are enabled. By echoing "0" to this file, all

Documentation/trace/ftrace.txt

+142 −91
Original line number Diff line number Diff line
@@ -7,7 +7,6 @@ Copyright 2008 Red Hat Inc. 
               (dual licensed under the GPL v2)

Reviewers:   Elias Oltmanns, Randy Dunlap, Andrew Morton,

	     John Kacur, and David Teigland.



Written for: 2.6.28-rc2



Introduction
@@ -33,13 +32,26 @@ The File System 
Ftrace uses the debugfs file system to hold the control files as

well as the files to display output.



To mount the debugfs system:

When debugfs is configured into the kernel (which selecting any ftrace

option will do) the directory /sys/kernel/debug will be created. To mount

this directory, you can add to your /etc/fstab file:



 debugfs       /sys/kernel/debug          debugfs defaults        0       0



Or you can mount it at run time with:



  # mkdir /debug

  # mount -t debugfs nodev /debug

 mount -t debugfs nodev /sys/kernel/debug



( Note: it is more common to mount at /sys/kernel/debug, but for

  simplicity this document will use /debug)

For quicker access to that directory you may want to make a soft link to

it:



 ln -s /sys/kernel/debug /debug



Any selected ftrace option will also create a directory called tracing

within the debugfs. The rest of the document will assume that you are in

the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate

on the files within that directory and not distract from the content with

the extended "/sys/kernel/debug/tracing" path name.



That's it! (assuming that you have ftrace configured into your kernel)
@@ -389,18 +401,18 @@ trace_options 
The trace_options file is used to control what gets printed in

the trace output. To see what is available, simply cat the file:



  cat /debug/tracing/trace_options

  cat trace_options

  print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \

  noblock nostacktrace nosched-tree nouserstacktrace nosym-userobj



To disable one of the options, echo in the option prepended with

"no".



  echo noprint-parent > /debug/tracing/trace_options

  echo noprint-parent > trace_options



To enable an option, leave off the "no".



  echo sym-offset > /debug/tracing/trace_options

  echo sym-offset > trace_options



Here are the available options:
@@ -476,11 +488,11 @@ sched_switch 
This tracer simply records schedule switches. Here is an example

of how to use it.



 # echo sched_switch > /debug/tracing/current_tracer

 # echo 1 > /debug/tracing/tracing_enabled

 # echo sched_switch > current_tracer

 # echo 1 > tracing_enabled

 # sleep 1

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/trace

 # echo 0 > tracing_enabled

 # cat trace



# tracer: sched_switch

#
@@ -583,13 +595,13 @@ new trace is saved. 
To reset the maximum, echo 0 into tracing_max_latency. Here is

an example:



 # echo irqsoff > /debug/tracing/current_tracer

 # echo 0 > /debug/tracing/tracing_max_latency

 # echo 1 > /debug/tracing/tracing_enabled

 # echo irqsoff > current_tracer

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/latency_trace

 # echo 0 > tracing_enabled

 # cat latency_trace

# tracer: irqsoff

#

irqsoff latency trace v1.1.5 on 2.6.26
@@ -690,13 +702,13 @@ Like the irqsoff tracer, it records the maximum latency for 
which preemption was disabled. The control of preemptoff tracer

is much like the irqsoff tracer.



 # echo preemptoff > /debug/tracing/current_tracer

 # echo 0 > /debug/tracing/tracing_max_latency

 # echo 1 > /debug/tracing/tracing_enabled

 # echo preemptoff > current_tracer

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/latency_trace

 # echo 0 > tracing_enabled

 # cat latency_trace

# tracer: preemptoff

#

preemptoff latency trace v1.1.5 on 2.6.26-rc8
@@ -837,13 +849,13 @@ tracer. 
Again, using this trace is much like the irqsoff and preemptoff

tracers.



 # echo preemptirqsoff > /debug/tracing/current_tracer

 # echo 0 > /debug/tracing/tracing_max_latency

 # echo 1 > /debug/tracing/tracing_enabled

 # echo preemptirqsoff > current_tracer

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # ls -ltr

 [...]

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/latency_trace

 # echo 0 > tracing_enabled

 # cat latency_trace

# tracer: preemptirqsoff

#

preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
@@ -999,12 +1011,12 @@ slightly differently than we did with the previous tracers. 
Instead of performing an 'ls', we will run 'sleep 1' under

'chrt' which changes the priority of the task.



 # echo wakeup > /debug/tracing/current_tracer

 # echo 0 > /debug/tracing/tracing_max_latency

 # echo 1 > /debug/tracing/tracing_enabled

 # echo wakeup > current_tracer

 # echo 0 > tracing_max_latency

 # echo 1 > tracing_enabled

 # chrt -f 5 sleep 1

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/latency_trace

 # echo 0 > tracing_enabled

 # cat latency_trace

# tracer: wakeup

#

wakeup latency trace v1.1.5 on 2.6.26-rc8
@@ -1114,11 +1126,11 @@ can be done from the debug file system. Make sure the 
ftrace_enabled is set; otherwise this tracer is a nop.



 # sysctl kernel.ftrace_enabled=1

 # echo function > /debug/tracing/current_tracer

 # echo 1 > /debug/tracing/tracing_enabled

 # echo function > current_tracer

 # echo 1 > tracing_enabled

 # usleep 1

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/trace

 # echo 0 > tracing_enabled

 # cat trace

# tracer: function

#

#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
@@ -1155,7 +1167,7 @@ int trace_fd; 
[...]

int main(int argc, char *argv[]) {

	[...]

	trace_fd = open("/debug/tracing/tracing_enabled", O_WRONLY);

	trace_fd = open(tracing_file("tracing_enabled"), O_WRONLY);

	[...]

	if (condition_hit()) {

		write(trace_fd, "0", 1);
@@ -1163,26 +1175,20 @@ int main(int argc, char *argv[]) { 
	[...]

}



Note: Here we hard coded the path name. The debugfs mount is not

guaranteed to be at /debug (and is more commonly at

/sys/kernel/debug). For simple one time traces, the above is

sufficent. For anything else, a search through /proc/mounts may

be needed to find where the debugfs file-system is mounted.





Single thread tracing

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



By writing into /debug/tracing/set_ftrace_pid you can trace a

By writing into set_ftrace_pid you can trace a

single thread. For example:



# cat /debug/tracing/set_ftrace_pid

# cat set_ftrace_pid

no pid

# echo 3111 > /debug/tracing/set_ftrace_pid

# cat /debug/tracing/set_ftrace_pid

# echo 3111 > set_ftrace_pid

# cat set_ftrace_pid

3111

# echo function > /debug/tracing/current_tracer

# cat /debug/tracing/trace | head

# echo function > current_tracer

# cat trace | head

 # tracer: function

 #

 #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
@@ -1193,8 +1199,8 @@ no pid 
     yum-updatesd-3111  [003]  1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel

     yum-updatesd-3111  [003]  1637.254685: fget_light <-do_sys_poll

     yum-updatesd-3111  [003]  1637.254686: pipe_poll <-do_sys_poll

# echo -1 > /debug/tracing/set_ftrace_pid

# cat /debug/tracing/trace |head

# echo -1 > set_ftrace_pid

# cat trace |head

 # tracer: function

 #

 #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
@@ -1216,6 +1222,51 @@ something like this simple program: 
#include <fcntl.h>

#include <unistd.h>



#define _STR(x) #x

#define STR(x) _STR(x)

#define MAX_PATH 256



const char *find_debugfs(void)

{

       static char debugfs[MAX_PATH+1];

       static int debugfs_found;

       char type[100];

       FILE *fp;



       if (debugfs_found)

               return debugfs;



       if ((fp = fopen("/proc/mounts","r")) == NULL) {

               perror("/proc/mounts");

               return NULL;

       }



       while (fscanf(fp, "%*s %"

                     STR(MAX_PATH)

                     "s %99s %*s %*d %*d\n",

                     debugfs, type) == 2) {

               if (strcmp(type, "debugfs") == 0)

                       break;

       }

       fclose(fp);



       if (strcmp(type, "debugfs") != 0) {

               fprintf(stderr, "debugfs not mounted");

               return NULL;

       }



       debugfs_found = 1;



       return debugfs;

}



const char *tracing_file(const char *file_name)

{

       static char trace_file[MAX_PATH+1];

       snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);

       return trace_file;

}



int main (int argc, char **argv)

{

        if (argc < 1)
@@ -1226,12 +1277,12 @@ int main (int argc, char **argv) 
                char line[64];

                int s;



                ffd = open("/debug/tracing/current_tracer", O_WRONLY);

                ffd = open(tracing_file("current_tracer"), O_WRONLY);

                if (ffd < 0)

                        exit(-1);

                write(ffd, "nop", 3);



                fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);

                fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);

                s = sprintf(line, "%d\n", getpid());

                write(fd, line, s);
@@ -1383,22 +1434,22 @@ want, depending on your needs. 
  tracing_cpu_mask file) or you might sometimes see unordered

  function calls while cpu tracing switch.



	hide: echo nofuncgraph-cpu > /debug/tracing/trace_options

	show: echo funcgraph-cpu > /debug/tracing/trace_options

	hide: echo nofuncgraph-cpu > trace_options

	show: echo funcgraph-cpu > trace_options



- The duration (function's time of execution) is displayed on

  the closing bracket line of a function or on the same line

  than the current function in case of a leaf one. It is default

  enabled.



	hide: echo nofuncgraph-duration > /debug/tracing/trace_options

	show: echo funcgraph-duration > /debug/tracing/trace_options

	hide: echo nofuncgraph-duration > trace_options

	show: echo funcgraph-duration > trace_options



- The overhead field precedes the duration field in case of

  reached duration thresholds.



	hide: echo nofuncgraph-overhead > /debug/tracing/trace_options

	show: echo funcgraph-overhead > /debug/tracing/trace_options

	hide: echo nofuncgraph-overhead > trace_options

	show: echo funcgraph-overhead > trace_options

	depends on: funcgraph-duration



  ie:
@@ -1427,8 +1478,8 @@ want, depending on your needs. 
- The task/pid field displays the thread cmdline and pid which

  executed the function. It is default disabled.



	hide: echo nofuncgraph-proc > /debug/tracing/trace_options

	show: echo funcgraph-proc > /debug/tracing/trace_options

	hide: echo nofuncgraph-proc > trace_options

	show: echo funcgraph-proc > trace_options



  ie:
@@ -1451,8 +1502,8 @@ want, depending on your needs. 
  system clock since it started. A snapshot of this time is

  given on each entry/exit of functions



	hide: echo nofuncgraph-abstime > /debug/tracing/trace_options

	show: echo funcgraph-abstime > /debug/tracing/trace_options

	hide: echo nofuncgraph-abstime > trace_options

	show: echo funcgraph-abstime > trace_options



  ie:
@@ -1549,7 +1600,7 @@ listed in: 


   available_filter_functions



 # cat /debug/tracing/available_filter_functions

 # cat available_filter_functions

put_prev_task_idle

kmem_cache_create

pick_next_task_rt
@@ -1561,12 +1612,12 @@ mutex_lock 
If I am only interested in sys_nanosleep and hrtimer_interrupt:



 # echo sys_nanosleep hrtimer_interrupt \

		> /debug/tracing/set_ftrace_filter

 # echo ftrace > /debug/tracing/current_tracer

 # echo 1 > /debug/tracing/tracing_enabled

		> set_ftrace_filter

 # echo ftrace > current_tracer

 # echo 1 > tracing_enabled

 # usleep 1

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/trace

 # echo 0 > tracing_enabled

 # cat trace

# tracer: ftrace

#

#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
@@ -1577,7 +1628,7 @@ If I am only interested in sys_nanosleep and hrtimer_interrupt: 


To see which functions are being traced, you can cat the file:



 # cat /debug/tracing/set_ftrace_filter

 # cat set_ftrace_filter

hrtimer_interrupt

sys_nanosleep
@@ -1597,7 +1648,7 @@ Note: It is better to use quotes to enclose the wild cards, 
      otherwise the shell may expand the parameters into names

      of files in the local directory.



 # echo 'hrtimer_*' > /debug/tracing/set_ftrace_filter

 # echo 'hrtimer_*' > set_ftrace_filter



Produces:
@@ -1618,7 +1669,7 @@ Produces: 


Notice that we lost the sys_nanosleep.



 # cat /debug/tracing/set_ftrace_filter

 # cat set_ftrace_filter

hrtimer_run_queues

hrtimer_run_pending

hrtimer_init
@@ -1644,17 +1695,17 @@ To append to the filters, use '>>' 
To clear out a filter so that all functions will be recorded

again:



 # echo > /debug/tracing/set_ftrace_filter

 # cat /debug/tracing/set_ftrace_filter

 # echo > set_ftrace_filter

 # cat set_ftrace_filter

 #



Again, now we want to append.



 # echo sys_nanosleep > /debug/tracing/set_ftrace_filter

 # cat /debug/tracing/set_ftrace_filter

 # echo sys_nanosleep > set_ftrace_filter

 # cat set_ftrace_filter

sys_nanosleep

 # echo 'hrtimer_*' >> /debug/tracing/set_ftrace_filter

 # cat /debug/tracing/set_ftrace_filter

 # echo 'hrtimer_*' >> set_ftrace_filter

 # cat set_ftrace_filter

hrtimer_run_queues

hrtimer_run_pending

hrtimer_init
@@ -1677,7 +1728,7 @@ hrtimer_init_sleeper 
The set_ftrace_notrace prevents those functions from being

traced.



 # echo '*preempt*' '*lock*' > /debug/tracing/set_ftrace_notrace

 # echo '*preempt*' '*lock*' > set_ftrace_notrace



Produces:
@@ -1767,13 +1818,13 @@ the effect on the tracing is different. Every read from 
trace_pipe is consumed. This means that subsequent reads will be

different. The trace is live.



 # echo function > /debug/tracing/current_tracer

 # cat /debug/tracing/trace_pipe > /tmp/trace.out &

 # echo function > current_tracer

 # cat trace_pipe > /tmp/trace.out &

[1] 4153

 # echo 1 > /debug/tracing/tracing_enabled

 # echo 1 > tracing_enabled

 # usleep 1

 # echo 0 > /debug/tracing/tracing_enabled

 # cat /debug/tracing/trace

 # echo 0 > tracing_enabled

 # cat trace

# tracer: function

#

#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
@@ -1809,7 +1860,7 @@ number listed is the number of entries that can be recorded per 
CPU. To know the full size, multiply the number of possible CPUS

with the number of entries.



 # cat /debug/tracing/buffer_size_kb

 # cat buffer_size_kb

1408 (units kilobytes)



Note, to modify this, you must have tracing completely disabled.
@@ -1817,18 +1868,18 @@ To do that, echo "nop" into the current_tracer. If the 
current_tracer is not set to "nop", an EINVAL error will be

returned.



 # echo nop > /debug/tracing/current_tracer

 # echo 10000 > /debug/tracing/buffer_size_kb

 # cat /debug/tracing/buffer_size_kb

 # echo nop > current_tracer

 # echo 10000 > buffer_size_kb

 # cat buffer_size_kb

10000 (units kilobytes)



The number of pages which will be allocated is limited to a

percentage of available memory. Allocating too much will produce

an error.



 # echo 1000000000000 > /debug/tracing/buffer_size_kb

 # echo 1000000000000 > buffer_size_kb

-bash: echo: write error: Cannot allocate memory

 # cat /debug/tracing/buffer_size_kb

 # cat buffer_size_kb

85



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