--- /dev/null
+From foo@baz Tue Apr 9 12:12:43 2002
+Date: Tue, 09 Apr 2002 12:14:34 -0700
+To: Greg KH <greg@kroah.com>
+From: Greg Kroah-Hartman <gregkh@suse.de>
+Subject: ftrace: remove unneeded documentation
+
+There is no ftrace in the 2.6.26 kernel release, so remove the
+documentation as it isn't needed.
+
+Cc: Steven Rostedt <rostedt@goodmis.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
+
+---
+ Documentation/ftrace.txt | 1353 -----------------------------------------------
+ 1 file changed, 1353 deletions(-)
+
+--- a/Documentation/ftrace.txt
++++ /dev/null
+@@ -1,1353 +0,0 @@
+- ftrace - Function Tracer
+- ========================
+-
+-Copyright 2008 Red Hat Inc.
+-Author: Steven Rostedt <srostedt@redhat.com>
+-
+-
+-Introduction
+-------------
+-
+-Ftrace is an internal tracer designed to help out developers and
+-designers of systems to find what is going on inside the kernel.
+-It can be used for debugging or analyzing latencies and performance
+-issues that take place outside of user-space.
+-
+-Although ftrace is the function tracer, it also includes an
+-infrastructure that allows for other types of tracing. Some of the
+-tracers that are currently in ftrace is a tracer to trace
+-context switches, the time it takes for a high priority task to
+-run after it was woken up, the time interrupts are disabled, and
+-more.
+-
+-
+-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:
+-
+- # mkdir /debug
+- # mount -t debugfs nodev /debug
+-
+-
+-That's it! (assuming that you have ftrace configured into your kernel)
+-
+-After mounting the debugfs, you can see a directory called
+-"tracing". This directory contains the control and output files
+-of ftrace. Here is a list of some of the key files:
+-
+-
+- Note: all time values are in microseconds.
+-
+- current_tracer : This is used to set or display the current tracer
+- that is configured.
+-
+- available_tracers : This holds the different types of tracers that
+- has been compiled into the kernel. The tracers
+- listed here can be configured by echoing in their
+- name into current_tracer.
+-
+- tracing_enabled : This sets or displays whether the current_tracer
+- is activated and tracing or not. Echo 0 into this
+- file to disable the tracer or 1 (or non-zero) to
+- enable it.
+-
+- trace : This file holds the output of the trace in a human readable
+- format.
+-
+- latency_trace : This file shows the same trace but the information
+- is organized more to display possible latencies
+- in the system.
+-
+- 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 isn't adding more data, they will display
+- the same information every time they are read.
+-
+- iter_ctrl : This file lets the user control the amount of data
+- that is displayed in one of the above output
+- files.
+-
+- trace_max_latency : 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)
+-
+- trace_entries : This sets or displays the number of trace
+- entries each CPU buffer can hold. The tracer buffers
+- are the same size for each CPU, so care must be
+- taken when modifying the trace_entries. The number
+- of actually entries will be the number given
+- times the number of possible CPUS. The buffers
+- are saved as individual pages, and the actual entries
+- will always be rounded up to entries per page.
+-
+- This can only be updated when the current_tracer
+- is set to "none".
+-
+- NOTE: It is planned on changing the allocated buffers
+- from being the number of possible CPUS to
+- the number of online CPUS.
+-
+- tracing_cpumask : This is a mask that lets the user only trace
+- on specified CPUS. The format is a hex string
+- representing the CPUS.
+-
+- set_ftrace_filter : When dynamic ftrace is configured in, the
+- code is dynamically modified to disable calling
+- of the function profiler (mcount). This lets
+- tracing be configured in with practically no overhead
+- in performance. This also has a side effect of
+- enabling or disabling specific functions to be
+- traced. Echoing in names of functions into this
+- file will limit the trace to only those files.
+-
+- set_ftrace_notrace: This has the opposite effect that
+- set_ftrace_filter has. Any function that is added
+- here will not be traced. If a function exists
+- in both set_ftrace_filter and set_ftrace_notrace
+- the function will _not_ bet traced.
+-
+- available_filter_functions : When a function is encountered the first
+- time by the dynamic tracer, it is recorded and
+- later the call is converted into a nop. This file
+- lists the functions that have been recorded
+- by the dynamic tracer and these functions can
+- be used to set the ftrace filter by the above
+- "set_ftrace_filter" file.
+-
+-
+-The Tracers
+------------
+-
+-Here are the list of current tracers that can be configured.
+-
+- ftrace - function tracer that uses mcount to trace all functions.
+- It is possible to filter out which functions that are
+- traced when dynamic ftrace is configured in.
+-
+- sched_switch - traces the context switches between tasks.
+-
+- irqsoff - traces the areas that disable interrupts and saves off
+- 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 with the latency_trace file.
+-
+- preemptoff - Similar to irqsoff but traces and records the time
+- preemption is disabled.
+-
+- preemptirqsoff - Similar to irqsoff and preemptoff, but traces and
+- records the largest time irqs and/or preemption is
+- disabled.
+-
+- wakeup - Traces and records the max latency that it takes for
+- the highest priority task to get scheduled after
+- it has been woken up.
+-
+- none - This is not a tracer. To remove all tracers from tracing
+- simply echo "none" into current_tracer.
+-
+-
+-Examples of using the tracer
+-----------------------------
+-
+-Here are typical examples of using the tracers with only controlling
+-them with the debugfs interface (without using any user-land utilities).
+-
+-Output format:
+---------------
+-
+-Here's an example of the output format of the file "trace"
+-
+- --------
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- bash-4251 [01] 10152.583854: path_put <-path_walk
+- bash-4251 [01] 10152.583855: dput <-path_put
+- bash-4251 [01] 10152.583855: _atomic_dec_and_lock <-dput
+- --------
+-
+-A header is printed with the trace that is represented. In this case
+-the tracer is "ftrace". Then a header showing the format. Task name
+-"bash", the task PID "4251", the CPU that it was running on
+-"01", the timestamp in <secs>.<usecs> format, the function name that was
+-traced "path_put" and the parent function that called this function
+-"path_walk".
+-
+-The sched_switch tracer also includes tracing of task wake ups and
+-context switches.
+-
+- ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 2916:115:S
+- ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 10:115:S
+- ksoftirqd/1-7 [01] 1453.070013: 7:115:R ==> 10:115:R
+- events/1-10 [01] 1453.070013: 10:115:S ==> 2916:115:R
+- kondemand/1-2916 [01] 1453.070013: 2916:115:S ==> 7:115:R
+- ksoftirqd/1-7 [01] 1453.070013: 7:115:S ==> 0:140:R
+-
+-Wake ups are represented by a "+" and the context switches show
+-"==>". The format is:
+-
+- Context switches:
+-
+- Previous task Next Task
+-
+- <pid>:<prio>:<state> ==> <pid>:<prio>:<state>
+-
+- Wake ups:
+-
+- Current task Task waking up
+-
+- <pid>:<prio>:<state> + <pid>:<prio>:<state>
+-
+-The prio is the internal kernel priority, which is inverse to the
+-priority that is usually displayed by user-space tools. Zero represents
+-the highest priority (99). Prio 100 starts the "nice" priorities with
+-100 being equal to nice -20 and 139 being nice 19. The prio "140" is
+-reserved for the idle task which is the lowest priority thread (pid 0).
+-
+-
+-Latency trace format
+---------------------
+-
+-For traces that display latency times, the latency_trace file gives
+-a bit more information to see why a latency happened. Here's a typical
+-trace.
+-
+-# tracer: irqsoff
+-#
+-irqsoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 97 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: apic_timer_interrupt
+- => ended at: do_softirq
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- <idle>-0 0d..1 0us+: trace_hardirqs_off_thunk (apic_timer_interrupt)
+- <idle>-0 0d.s. 97us : __do_softirq (do_softirq)
+- <idle>-0 0d.s1 98us : trace_hardirqs_on (do_softirq)
+-
+-
+-vim:ft=help
+-
+-
+-This shows that the current tracer is "irqsoff" tracing the time
+-interrupts are disabled. It gives the trace version and the kernel
+-this was executed on (2.6.26-rc8). Then it displays the max latency
+-in microsecs (97 us). The number of trace entries displayed
+-by the total number recorded (both are three: #3/3). The type of
+-preemption that was used (PREEMPT). VP, KP, SP, and HP are always zero
+-and reserved for later use. #P is the number of online CPUS (#P:2).
+-
+-The task is the process that was running when the latency happened.
+-(swapper pid: 0).
+-
+-The start and stop that caused the latencies:
+-
+- apic_timer_interrupt is where the interrupts were disabled.
+- do_softirq is where they were enabled again.
+-
+-The next lines after the header are the trace itself. The header
+-explains which is which.
+-
+- cmd: The name of the process in the trace.
+-
+- pid: The PID of that process.
+-
+- CPU#: The CPU that the process was running on.
+-
+- irqs-off: 'd' interrupts are disabled. '.' otherwise.
+-
+- need-resched: 'N' task need_resched is set, '.' otherwise.
+-
+- hardirq/softirq:
+- 'H' - hard irq happened inside a softirq.
+- 'h' - hard irq is running
+- 's' - soft irq is running
+- '.' - normal context.
+-
+- preempt-depth: The level of preempt_disabled
+-
+-The above is mostly meaningful for kernel developers.
+-
+- time: This differs from the trace output where as the trace output
+- contained a absolute timestamp. This timestamp is relative
+- to the start of the first entry in the the trace.
+-
+- 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.
+- The marks is determined by the difference between this
+- current trace and the next trace.
+- '!' - greater than preempt_mark_thresh (default 100)
+- '+' - greater than 1 microsecond
+- ' ' - less than or equal to 1 microsecond.
+-
+- The rest is the same as the 'trace' file.
+-
+-
+-iter_ctrl
+----------
+-
+-The iter_ctrl file is used to control what gets printed in the trace
+-output. To see what is available, simply cat the file:
+-
+- cat /debug/tracing/iter_ctrl
+- print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \
+- noblock nostacktrace nosched-tree
+-
+-To disable one of the options, echo in the option appended with "no".
+-
+- echo noprint-parent > /debug/tracing/iter_ctrl
+-
+-To enable an option, leave off the "no".
+-
+- echo sym-offest > /debug/tracing/iter_ctrl
+-
+-Here are the available options:
+-
+- print-parent - On function traces, display the calling function
+- as well as the function being traced.
+-
+- print-parent:
+- bash-4000 [01] 1477.606694: simple_strtoul <-strict_strtoul
+-
+- noprint-parent:
+- bash-4000 [01] 1477.606694: simple_strtoul
+-
+-
+- sym-offset - Display not only the function name, but also the offset
+- in the function. For example, instead of seeing just
+- "ktime_get" you will see "ktime_get+0xb/0x20"
+-
+- sym-offset:
+- bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
+-
+- sym-addr - this will also display the function address as well as
+- the function name.
+-
+- sym-addr:
+- bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
+-
+- verbose - This deals with the latency_trace file.
+-
+- bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
+- (+0.000ms): simple_strtoul (strict_strtoul)
+-
+- raw - This will display raw numbers. This option is best for use with
+- user applications that can translate the raw numbers better than
+- having it done in the kernel.
+-
+- hex - similar to raw, but the numbers will be in a hexadecimal format.
+-
+- bin - This will print out the formats in raw binary.
+-
+- block - TBD (needs update)
+-
+- stacktrace - This is one of the options that changes the trace itself.
+- When a trace is recorded, so is the stack of functions.
+- This allows for back traces of trace sites.
+-
+- sched-tree - TBD (any users??)
+-
+-
+-sched_switch
+-------------
+-
+-This tracer simply records schedule switches. Here's an example
+-on how to implement it.
+-
+- # echo sched_switch > /debug/tracing/current_tracer
+- # echo 1 > /debug/tracing/tracing_enabled
+- # sleep 1
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/trace
+-
+-# tracer: sched_switch
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- bash-3997 [01] 240.132281: 3997:120:R + 4055:120:R
+- bash-3997 [01] 240.132284: 3997:120:R ==> 4055:120:R
+- sleep-4055 [01] 240.132371: 4055:120:S ==> 3997:120:R
+- bash-3997 [01] 240.132454: 3997:120:R + 4055:120:S
+- bash-3997 [01] 240.132457: 3997:120:R ==> 4055:120:R
+- sleep-4055 [01] 240.132460: 4055:120:D ==> 3997:120:R
+- bash-3997 [01] 240.132463: 3997:120:R + 4055:120:D
+- bash-3997 [01] 240.132465: 3997:120:R ==> 4055:120:R
+- <idle>-0 [00] 240.132589: 0:140:R + 4:115:S
+- <idle>-0 [00] 240.132591: 0:140:R ==> 4:115:R
+- ksoftirqd/0-4 [00] 240.132595: 4:115:S ==> 0:140:R
+- <idle>-0 [00] 240.132598: 0:140:R + 4:115:S
+- <idle>-0 [00] 240.132599: 0:140:R ==> 4:115:R
+- ksoftirqd/0-4 [00] 240.132603: 4:115:S ==> 0:140:R
+- sleep-4055 [01] 240.133058: 4055:120:S ==> 3997:120:R
+- [...]
+-
+-
+-As we have discussed previously about this format, the header shows
+-the name of the trace and points to the options. The "FUNCTION"
+-is a misnomer since here it represents the wake ups and context
+-switches.
+-
+-The sched_switch only lists the wake ups (represented with '+')
+-and context switches ('==>') with the previous task or current
+-first followed by the next task or task waking up. The format for both
+-of these is PID:KERNEL-PRIO:TASK-STATE. Remember that the KERNEL-PRIO
+-is the inverse of the actual priority with zero (0) being the highest
+-priority and the nice values starting at 100 (nice -20). Below is
+-a quick chart to map the kernel priority to user land priorities.
+-
+- Kernel priority: 0 to 99 ==> user RT priority 99 to 0
+- Kernel priority: 100 to 139 ==> user nice -20 to 19
+- Kernel priority: 140 ==> idle task priority
+-
+-The task states are:
+-
+- R - running : wants to run, may not actually be running
+- S - sleep : process is waiting to be woken up (handles signals)
+- D - deep sleep : process must be woken up (ignores signals)
+- T - stopped : process suspended
+- t - traced : process is being traced (with something like gdb)
+- Z - zombie : process waiting to be cleaned up
+- X - unknown
+-
+-
+-ftrace_enabled
+---------------
+-
+-The following tracers give different output depending on whether
+-or not the sysctl ftrace_enabled is set. To set ftrace_enabled,
+-one can either use the sysctl function or set it via the proc
+-file system interface.
+-
+- sysctl kernel.ftrace_enabled=1
+-
+- or
+-
+- echo 1 > /proc/sys/kernel/ftrace_enabled
+-
+-To disable ftrace_enabled simply replace the '1' with '0' in
+-the above commands.
+-
+-When ftrace_enabled is set the tracers will also record the functions
+-that are within the trace. The descriptions of the tracers
+-will also show an example with ftrace enabled.
+-
+-
+-irqsoff
+--------
+-
+-When interrupts are disabled, the CPU can not react to any other
+-external event (besides NMIs and SMIs). This prevents the timer
+-interrupt from triggering or the mouse interrupt from letting the
+-kernel know of a new mouse event. The result is a latency with the
+-reaction time.
+-
+-The irqsoff tracer tracks the time interrupts are disabled and when
+-they are re-enabled. When a new maximum latency is hit, it saves off
+-the trace so that it may be retrieved at a later time. Every time a
+-new maximum in reached, the old saved trace is discarded and the new
+-trace is saved.
+-
+-To reset the maximum, echo 0 into tracing_max_latency. Here's an
+-example:
+-
+- # echo irqsoff > /debug/tracing/current_tracer
+- # echo 0 > /debug/tracing/tracing_max_latency
+- # echo 1 > /debug/tracing/tracing_enabled
+- # ls -ltr
+- [...]
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/latency_trace
+-# tracer: irqsoff
+-#
+-irqsoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 6 us, #3/3, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: bash-4269 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: copy_page_range
+- => ended at: copy_page_range
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- bash-4269 1...1 0us+: _spin_lock (copy_page_range)
+- bash-4269 1...1 7us : _spin_unlock (copy_page_range)
+- bash-4269 1...2 7us : trace_preempt_on (copy_page_range)
+-
+-
+-vim:ft=help
+-
+-Here we see that that we had a latency of 6 microsecs (which is
+-very good). The spin_lock in copy_page_range disabled interrupts.
+-The difference between the 6 and the displayed timestamp 7us is
+-because the clock must have incremented between the time of recording
+-the max latency and recording the function that had that latency.
+-
+-Note the above had ftrace_enabled not set. If we set the ftrace_enabled
+-we get a much larger output:
+-
+-# tracer: irqsoff
+-#
+-irqsoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 50 us, #101/101, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: ls-4339 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: __alloc_pages_internal
+- => ended at: __alloc_pages_internal
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- ls-4339 0...1 0us+: get_page_from_freelist (__alloc_pages_internal)
+- ls-4339 0d..1 3us : rmqueue_bulk (get_page_from_freelist)
+- ls-4339 0d..1 3us : _spin_lock (rmqueue_bulk)
+- ls-4339 0d..1 4us : add_preempt_count (_spin_lock)
+- ls-4339 0d..2 4us : __rmqueue (rmqueue_bulk)
+- ls-4339 0d..2 5us : __rmqueue_smallest (__rmqueue)
+- ls-4339 0d..2 5us : __mod_zone_page_state (__rmqueue_smallest)
+- ls-4339 0d..2 6us : __rmqueue (rmqueue_bulk)
+- ls-4339 0d..2 6us : __rmqueue_smallest (__rmqueue)
+- ls-4339 0d..2 7us : __mod_zone_page_state (__rmqueue_smallest)
+- ls-4339 0d..2 7us : __rmqueue (rmqueue_bulk)
+- ls-4339 0d..2 8us : __rmqueue_smallest (__rmqueue)
+-[...]
+- ls-4339 0d..2 46us : __rmqueue_smallest (__rmqueue)
+- ls-4339 0d..2 47us : __mod_zone_page_state (__rmqueue_smallest)
+- ls-4339 0d..2 47us : __rmqueue (rmqueue_bulk)
+- ls-4339 0d..2 48us : __rmqueue_smallest (__rmqueue)
+- ls-4339 0d..2 48us : __mod_zone_page_state (__rmqueue_smallest)
+- ls-4339 0d..2 49us : _spin_unlock (rmqueue_bulk)
+- ls-4339 0d..2 49us : sub_preempt_count (_spin_unlock)
+- ls-4339 0d..1 50us : get_page_from_freelist (__alloc_pages_internal)
+- ls-4339 0d..2 51us : trace_hardirqs_on (__alloc_pages_internal)
+-
+-
+-vim:ft=help
+-
+-
+-Here we traced a 50 microsecond latency. But we also see all the
+-functions that were called during that time. Note that enabling
+-function tracing we endure an added overhead. This overhead may
+-extend the latency times. But never the less, this trace has provided
+-some very helpful debugging.
+-
+-
+-preemptoff
+-----------
+-
+-When preemption is disabled we may be able to receive interrupts but
+-the task can not be preempted and a higher priority task must wait
+-for preemption to be enabled again before it can preempt a lower
+-priority task.
+-
+-The preemptoff tracer traces the places that disables preemption.
+-Like the irqsoff, it records the maximum latency that preemption
+-was disabled. The control of preemptoff is much like the irqsoff.
+-
+- # echo preemptoff > /debug/tracing/current_tracer
+- # echo 0 > /debug/tracing/tracing_max_latency
+- # echo 1 > /debug/tracing/tracing_enabled
+- # ls -ltr
+- [...]
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/latency_trace
+-# tracer: preemptoff
+-#
+-preemptoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 29 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: do_IRQ
+- => ended at: __do_softirq
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- sshd-4261 0d.h. 0us+: irq_enter (do_IRQ)
+- sshd-4261 0d.s. 29us : _local_bh_enable (__do_softirq)
+- sshd-4261 0d.s1 30us : trace_preempt_on (__do_softirq)
+-
+-
+-vim:ft=help
+-
+-This has some more changes. Preemption was disabled when an interrupt
+-came in (notice the 'h'), and was enabled while doing a softirq.
+-(notice the 's'). But we also see that interrupts have been disabled
+-when entering the preempt off section and leaving it (the 'd').
+-We do not know if interrupts were enabled in the mean time.
+-
+-# tracer: preemptoff
+-#
+-preemptoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 63 us, #87/87, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: remove_wait_queue
+- => ended at: __do_softirq
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- sshd-4261 0d..1 0us : _spin_lock_irqsave (remove_wait_queue)
+- sshd-4261 0d..1 1us : _spin_unlock_irqrestore (remove_wait_queue)
+- sshd-4261 0d..1 2us : do_IRQ (common_interrupt)
+- sshd-4261 0d..1 2us : irq_enter (do_IRQ)
+- sshd-4261 0d..1 2us : idle_cpu (irq_enter)
+- sshd-4261 0d..1 3us : add_preempt_count (irq_enter)
+- sshd-4261 0d.h1 3us : idle_cpu (irq_enter)
+- sshd-4261 0d.h. 4us : handle_fasteoi_irq (do_IRQ)
+-[...]
+- sshd-4261 0d.h. 12us : add_preempt_count (_spin_lock)
+- sshd-4261 0d.h1 12us : ack_ioapic_quirk_irq (handle_fasteoi_irq)
+- sshd-4261 0d.h1 13us : move_native_irq (ack_ioapic_quirk_irq)
+- sshd-4261 0d.h1 13us : _spin_unlock (handle_fasteoi_irq)
+- sshd-4261 0d.h1 14us : sub_preempt_count (_spin_unlock)
+- sshd-4261 0d.h1 14us : irq_exit (do_IRQ)
+- sshd-4261 0d.h1 15us : sub_preempt_count (irq_exit)
+- sshd-4261 0d..2 15us : do_softirq (irq_exit)
+- sshd-4261 0d... 15us : __do_softirq (do_softirq)
+- sshd-4261 0d... 16us : __local_bh_disable (__do_softirq)
+- sshd-4261 0d... 16us+: add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s4 20us : add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s4 21us : sub_preempt_count (local_bh_enable)
+- sshd-4261 0d.s5 21us : sub_preempt_count (local_bh_enable)
+-[...]
+- sshd-4261 0d.s6 41us : add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s6 42us : sub_preempt_count (local_bh_enable)
+- sshd-4261 0d.s7 42us : sub_preempt_count (local_bh_enable)
+- sshd-4261 0d.s5 43us : add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s5 43us : sub_preempt_count (local_bh_enable_ip)
+- sshd-4261 0d.s6 44us : sub_preempt_count (local_bh_enable_ip)
+- sshd-4261 0d.s5 44us : add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s5 45us : sub_preempt_count (local_bh_enable)
+-[...]
+- sshd-4261 0d.s. 63us : _local_bh_enable (__do_softirq)
+- sshd-4261 0d.s1 64us : trace_preempt_on (__do_softirq)
+-
+-
+-The above is an example of the preemptoff trace with ftrace_enabled
+-set. Here we see that interrupts were disabled the entire time.
+-The irq_enter code lets us know that we entered an interrupt 'h'.
+-Before that, the functions being traced still show that it is not
+-in an interrupt, but we can see by the functions themselves that
+-this is not the case.
+-
+-Notice that the __do_softirq when called doesn't have a preempt_count.
+-It may seem that we missed a preempt enabled. What really happened
+-is that the preempt count is held on the threads stack and we
+-switched to the softirq stack (4K stacks in effect). The code
+-does not copy the preempt count, but because interrupts are disabled
+-we don't need to worry about it. Having a tracer like this is good
+-to let people know what really happens inside the kernel.
+-
+-
+-preemptirqsoff
+---------------
+-
+-Knowing the locations that have interrupts disabled or preemption
+-disabled for the longest times is helpful. But sometimes we would
+-like to know when either preemption and/or interrupts are disabled.
+-
+-The following code:
+-
+- local_irq_disable();
+- call_function_with_irqs_off();
+- preempt_disable();
+- call_function_with_irqs_and_preemption_off();
+- local_irq_enable();
+- call_function_with_preemption_off();
+- preempt_enable();
+-
+-The irqsoff tracer will record the total length of
+-call_function_with_irqs_off() and
+-call_function_with_irqs_and_preemption_off().
+-
+-The preemptoff tracer will record the total length of
+-call_function_with_irqs_and_preemption_off() and
+-call_function_with_preemption_off().
+-
+-But neither will trace the time that interrupts and/or preemption
+-is disabled. This total time is the time that we can not schedule.
+-To record this time, use the preemptirqsoff tracer.
+-
+-Again, using this trace is much like the irqsoff and preemptoff tracers.
+-
+- # echo preemptoff > /debug/tracing/current_tracer
+- # echo 0 > /debug/tracing/tracing_max_latency
+- # echo 1 > /debug/tracing/tracing_enabled
+- # ls -ltr
+- [...]
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/latency_trace
+-# tracer: preemptirqsoff
+-#
+-preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 293 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: ls-4860 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: apic_timer_interrupt
+- => ended at: __do_softirq
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- ls-4860 0d... 0us!: trace_hardirqs_off_thunk (apic_timer_interrupt)
+- ls-4860 0d.s. 294us : _local_bh_enable (__do_softirq)
+- ls-4860 0d.s1 294us : trace_preempt_on (__do_softirq)
+-
+-
+-vim:ft=help
+-
+-
+-The trace_hardirqs_off_thunk is called from assembly on x86 when
+-interrupts are disabled in the assembly code. Without the function
+-tracing, we don't know if interrupts were enabled within the preemption
+-points. We do see that it started with preemption enabled.
+-
+-Here is a trace with ftrace_enabled set:
+-
+-
+-# tracer: preemptirqsoff
+-#
+-preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 105 us, #183/183, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0)
+- -----------------
+- => started at: write_chan
+- => ended at: __do_softirq
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- ls-4473 0.N.. 0us : preempt_schedule (write_chan)
+- ls-4473 0dN.1 1us : _spin_lock (schedule)
+- ls-4473 0dN.1 2us : add_preempt_count (_spin_lock)
+- ls-4473 0d..2 2us : put_prev_task_fair (schedule)
+-[...]
+- ls-4473 0d..2 13us : set_normalized_timespec (ktime_get_ts)
+- ls-4473 0d..2 13us : __switch_to (schedule)
+- sshd-4261 0d..2 14us : finish_task_switch (schedule)
+- sshd-4261 0d..2 14us : _spin_unlock_irq (finish_task_switch)
+- sshd-4261 0d..1 15us : add_preempt_count (_spin_lock_irqsave)
+- sshd-4261 0d..2 16us : _spin_unlock_irqrestore (hrtick_set)
+- sshd-4261 0d..2 16us : do_IRQ (common_interrupt)
+- sshd-4261 0d..2 17us : irq_enter (do_IRQ)
+- sshd-4261 0d..2 17us : idle_cpu (irq_enter)
+- sshd-4261 0d..2 18us : add_preempt_count (irq_enter)
+- sshd-4261 0d.h2 18us : idle_cpu (irq_enter)
+- sshd-4261 0d.h. 18us : handle_fasteoi_irq (do_IRQ)
+- sshd-4261 0d.h. 19us : _spin_lock (handle_fasteoi_irq)
+- sshd-4261 0d.h. 19us : add_preempt_count (_spin_lock)
+- sshd-4261 0d.h1 20us : _spin_unlock (handle_fasteoi_irq)
+- sshd-4261 0d.h1 20us : sub_preempt_count (_spin_unlock)
+-[...]
+- sshd-4261 0d.h1 28us : _spin_unlock (handle_fasteoi_irq)
+- sshd-4261 0d.h1 29us : sub_preempt_count (_spin_unlock)
+- sshd-4261 0d.h2 29us : irq_exit (do_IRQ)
+- sshd-4261 0d.h2 29us : sub_preempt_count (irq_exit)
+- sshd-4261 0d..3 30us : do_softirq (irq_exit)
+- sshd-4261 0d... 30us : __do_softirq (do_softirq)
+- sshd-4261 0d... 31us : __local_bh_disable (__do_softirq)
+- sshd-4261 0d... 31us+: add_preempt_count (__local_bh_disable)
+- sshd-4261 0d.s4 34us : add_preempt_count (__local_bh_disable)
+-[...]
+- sshd-4261 0d.s3 43us : sub_preempt_count (local_bh_enable_ip)
+- sshd-4261 0d.s4 44us : sub_preempt_count (local_bh_enable_ip)
+- sshd-4261 0d.s3 44us : smp_apic_timer_interrupt (apic_timer_interrupt)
+- sshd-4261 0d.s3 45us : irq_enter (smp_apic_timer_interrupt)
+- sshd-4261 0d.s3 45us : idle_cpu (irq_enter)
+- sshd-4261 0d.s3 46us : add_preempt_count (irq_enter)
+- sshd-4261 0d.H3 46us : idle_cpu (irq_enter)
+- sshd-4261 0d.H3 47us : hrtimer_interrupt (smp_apic_timer_interrupt)
+- sshd-4261 0d.H3 47us : ktime_get (hrtimer_interrupt)
+-[...]
+- sshd-4261 0d.H3 81us : tick_program_event (hrtimer_interrupt)
+- sshd-4261 0d.H3 82us : ktime_get (tick_program_event)
+- sshd-4261 0d.H3 82us : ktime_get_ts (ktime_get)
+- sshd-4261 0d.H3 83us : getnstimeofday (ktime_get_ts)
+- sshd-4261 0d.H3 83us : set_normalized_timespec (ktime_get_ts)
+- sshd-4261 0d.H3 84us : clockevents_program_event (tick_program_event)
+- sshd-4261 0d.H3 84us : lapic_next_event (clockevents_program_event)
+- sshd-4261 0d.H3 85us : irq_exit (smp_apic_timer_interrupt)
+- sshd-4261 0d.H3 85us : sub_preempt_count (irq_exit)
+- sshd-4261 0d.s4 86us : sub_preempt_count (irq_exit)
+- sshd-4261 0d.s3 86us : add_preempt_count (__local_bh_disable)
+-[...]
+- sshd-4261 0d.s1 98us : sub_preempt_count (net_rx_action)
+- sshd-4261 0d.s. 99us : add_preempt_count (_spin_lock_irq)
+- sshd-4261 0d.s1 99us+: _spin_unlock_irq (run_timer_softirq)
+- sshd-4261 0d.s. 104us : _local_bh_enable (__do_softirq)
+- sshd-4261 0d.s. 104us : sub_preempt_count (_local_bh_enable)
+- sshd-4261 0d.s. 105us : _local_bh_enable (__do_softirq)
+- sshd-4261 0d.s1 105us : trace_preempt_on (__do_softirq)
+-
+-
+-This is a very interesting trace. It started with the preemption of
+-the ls task. We see that the task had the "need_resched" bit set
+-with the 'N' in the trace. Interrupts are disabled in the spin_lock
+-and the trace started. We see that a schedule took place to run
+-sshd. When the interrupts were enabled we took an interrupt.
+-On return of the interrupt the softirq ran. We took another interrupt
+-while running the softirq as we see with the capital 'H'.
+-
+-
+-wakeup
+-------
+-
+-In Real-Time environment it is very important to know the wakeup
+-time it takes for the highest priority task that wakes up to the
+-time it executes. This is also known as "schedule latency".
+-I stress the point that this is about RT tasks. It is also important
+-to know the scheduling latency of non-RT tasks, but the average
+-schedule latency is better for non-RT tasks. Tools like
+-LatencyTop is more appropriate for such measurements.
+-
+-Real-Time environments is interested in the worst case latency.
+-That is the longest latency it takes for something to happen, and
+-not the average. We can have a very fast scheduler that may only
+-have a large latency once in a while, but that would not work well
+-with Real-Time tasks. The wakeup tracer was designed to record
+-the worst case wakeups of RT tasks. Non-RT tasks are not recorded
+-because the tracer only records one worst case and tracing non-RT
+-tasks that are unpredictable will overwrite the worst case latency
+-of RT tasks.
+-
+-Since this tracer only deals with RT tasks, we will run this slightly
+-different 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
+- # chrt -f 5 sleep 1
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/latency_trace
+-# tracer: wakeup
+-#
+-wakeup latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 4 us, #2/2, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: sleep-4901 (uid:0 nice:0 policy:1 rt_prio:5)
+- -----------------
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+- <idle>-0 1d.h4 0us+: try_to_wake_up (wake_up_process)
+- <idle>-0 1d..4 4us : schedule (cpu_idle)
+-
+-
+-vim:ft=help
+-
+-
+-Running this on an idle system we see that it only took 4 microseconds
+-to perform the task switch. Note, since the trace marker in the
+-schedule is before the actual "switch" we stop the tracing when
+-the recorded task is about to schedule in. This may change if
+-we add a new marker at the end of the scheduler.
+-
+-Notice that the recorded task is 'sleep' with the PID of 4901 and it
+-has an rt_prio of 5. This priority is user-space priority and not
+-the internal kernel priority. The policy is 1 for SCHED_FIFO and 2
+-for SCHED_RR.
+-
+-Doing the same with chrt -r 5 and ftrace_enabled set.
+-
+-# tracer: wakeup
+-#
+-wakeup latency trace v1.1.5 on 2.6.26-rc8
+---------------------------------------------------------------------
+- latency: 50 us, #60/60, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
+- -----------------
+- | task: sleep-4068 (uid:0 nice:0 policy:2 rt_prio:5)
+- -----------------
+-
+-# _------=> CPU#
+-# / _-----=> irqs-off
+-# | / _----=> need-resched
+-# || / _---=> hardirq/softirq
+-# ||| / _--=> preempt-depth
+-# |||| /
+-# ||||| delay
+-# cmd pid ||||| time | caller
+-# \ / ||||| \ | /
+-ksoftirq-7 1d.H3 0us : try_to_wake_up (wake_up_process)
+-ksoftirq-7 1d.H4 1us : sub_preempt_count (marker_probe_cb)
+-ksoftirq-7 1d.H3 2us : check_preempt_wakeup (try_to_wake_up)
+-ksoftirq-7 1d.H3 3us : update_curr (check_preempt_wakeup)
+-ksoftirq-7 1d.H3 4us : calc_delta_mine (update_curr)
+-ksoftirq-7 1d.H3 5us : __resched_task (check_preempt_wakeup)
+-ksoftirq-7 1d.H3 6us : task_wake_up_rt (try_to_wake_up)
+-ksoftirq-7 1d.H3 7us : _spin_unlock_irqrestore (try_to_wake_up)
+-[...]
+-ksoftirq-7 1d.H2 17us : irq_exit (smp_apic_timer_interrupt)
+-ksoftirq-7 1d.H2 18us : sub_preempt_count (irq_exit)
+-ksoftirq-7 1d.s3 19us : sub_preempt_count (irq_exit)
+-ksoftirq-7 1..s2 20us : rcu_process_callbacks (__do_softirq)
+-[...]
+-ksoftirq-7 1..s2 26us : __rcu_process_callbacks (rcu_process_callbacks)
+-ksoftirq-7 1d.s2 27us : _local_bh_enable (__do_softirq)
+-ksoftirq-7 1d.s2 28us : sub_preempt_count (_local_bh_enable)
+-ksoftirq-7 1.N.3 29us : sub_preempt_count (ksoftirqd)
+-ksoftirq-7 1.N.2 30us : _cond_resched (ksoftirqd)
+-ksoftirq-7 1.N.2 31us : __cond_resched (_cond_resched)
+-ksoftirq-7 1.N.2 32us : add_preempt_count (__cond_resched)
+-ksoftirq-7 1.N.2 33us : schedule (__cond_resched)
+-ksoftirq-7 1.N.2 33us : add_preempt_count (schedule)
+-ksoftirq-7 1.N.3 34us : hrtick_clear (schedule)
+-ksoftirq-7 1dN.3 35us : _spin_lock (schedule)
+-ksoftirq-7 1dN.3 36us : add_preempt_count (_spin_lock)
+-ksoftirq-7 1d..4 37us : put_prev_task_fair (schedule)
+-ksoftirq-7 1d..4 38us : update_curr (put_prev_task_fair)
+-[...]
+-ksoftirq-7 1d..5 47us : _spin_trylock (tracing_record_cmdline)
+-ksoftirq-7 1d..5 48us : add_preempt_count (_spin_trylock)
+-ksoftirq-7 1d..6 49us : _spin_unlock (tracing_record_cmdline)
+-ksoftirq-7 1d..6 49us : sub_preempt_count (_spin_unlock)
+-ksoftirq-7 1d..4 50us : schedule (__cond_resched)
+-
+-The interrupt went off while running ksoftirqd. This task runs at
+-SCHED_OTHER. Why didn't we see the 'N' set early? This may be
+-a harmless bug with x86_32 and 4K stacks. The need_reched() function
+-that tests if we need to reschedule looks on the actual stack.
+-Where as the setting of the NEED_RESCHED bit happens on the
+-task's stack. But because we are in a hard interrupt, the test
+-is with the interrupts stack which has that to be false. We don't
+-see the 'N' until we switch back to the task's stack.
+-
+-ftrace
+-------
+-
+-ftrace is not only the name of the tracing infrastructure, but it
+-is also a name of one of the tracers. The tracer is the function
+-tracer. Enabling the function tracer 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 ftrace > /debug/tracing/current_tracer
+- # echo 1 > /debug/tracing/tracing_enabled
+- # usleep 1
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/trace
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- bash-4003 [00] 123.638713: finish_task_switch <-schedule
+- bash-4003 [00] 123.638714: _spin_unlock_irq <-finish_task_switch
+- bash-4003 [00] 123.638714: sub_preempt_count <-_spin_unlock_irq
+- bash-4003 [00] 123.638715: hrtick_set <-schedule
+- bash-4003 [00] 123.638715: _spin_lock_irqsave <-hrtick_set
+- bash-4003 [00] 123.638716: add_preempt_count <-_spin_lock_irqsave
+- bash-4003 [00] 123.638716: _spin_unlock_irqrestore <-hrtick_set
+- bash-4003 [00] 123.638717: sub_preempt_count <-_spin_unlock_irqrestore
+- bash-4003 [00] 123.638717: hrtick_clear <-hrtick_set
+- bash-4003 [00] 123.638718: sub_preempt_count <-schedule
+- bash-4003 [00] 123.638718: sub_preempt_count <-preempt_schedule
+- bash-4003 [00] 123.638719: wait_for_completion <-__stop_machine_run
+- bash-4003 [00] 123.638719: wait_for_common <-wait_for_completion
+- bash-4003 [00] 123.638720: _spin_lock_irq <-wait_for_common
+- bash-4003 [00] 123.638720: add_preempt_count <-_spin_lock_irq
+-[...]
+-
+-
+-Note: It is sometimes better to enable or disable tracing directly from
+-a program, because the buffer may be overflowed by the echo commands
+-before you get to the point you want to trace. It is also easier to
+-stop the tracing at the point that you hit the part that you are
+-interested in. Since the ftrace buffer is a ring buffer with the
+-oldest data being overwritten, usually it is sufficient to start the
+-tracer with an echo command but have you code stop it. Something
+-like the following is usually appropriate for this.
+-
+-int trace_fd;
+-[...]
+-int main(int argc, char *argv[]) {
+- [...]
+- trace_fd = open("/debug/tracing/tracing_enabled", O_WRONLY);
+- [...]
+- if (condition_hit()) {
+- write(trace_fd, "0", 1);
+- }
+- [...]
+-}
+-
+-
+-dynamic ftrace
+---------------
+-
+-If CONFIG_DYNAMIC_FTRACE is set, then the system will run with
+-virtually no overhead when function tracing is disabled. The way
+-this works is the mcount function call (placed at the start of
+-every kernel function, produced by the -pg switch in gcc), starts
+-of pointing to a simple return.
+-
+-When dynamic ftrace is initialized, it calls kstop_machine to make it
+-act like a uniprocessor so that it can freely modify code without
+-worrying about other processors executing that same code. At
+-initialization, the mcount calls are change to call a "record_ip"
+-function. After this, the first time a kernel function is called,
+-it has the calling address saved in a hash table.
+-
+-Later on the ftraced kernel thread is awoken and will again call
+-kstop_machine if new functions have been recorded. The ftraced thread
+-will change all calls to mcount to "nop". Just calling mcount
+-and having mcount return has shown a 10% overhead. By converting
+-it to a nop, there is no recordable overhead to the system.
+-
+-One special side-effect to the recording of the functions being
+-traced, is that we can now selectively choose which functions we
+-want to trace and which ones we want the mcount calls to remain as
+-nops.
+-
+-Two files that contain to the enabling and disabling of recorded
+-functions are:
+-
+- set_ftrace_filter
+-
+-and
+-
+- set_ftrace_notrace
+-
+-A list of available functions that you can add to this files is listed
+-in:
+-
+- available_filter_functions
+-
+- # cat /debug/tracing/available_filter_functions
+-put_prev_task_idle
+-kmem_cache_create
+-pick_next_task_rt
+-get_online_cpus
+-pick_next_task_fair
+-mutex_lock
+-[...]
+-
+-If I'm 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
+- # usleep 1
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/trace
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- usleep-4134 [00] 1317.070017: hrtimer_interrupt <-smp_apic_timer_interrupt
+- usleep-4134 [00] 1317.070111: sys_nanosleep <-syscall_call
+- <idle>-0 [00] 1317.070115: hrtimer_interrupt <-smp_apic_timer_interrupt
+-
+-To see what functions are being traced, you can cat the file:
+-
+- # cat /debug/tracing/set_ftrace_filter
+-hrtimer_interrupt
+-sys_nanosleep
+-
+-
+-Perhaps this isn't enough. The filters also allow simple wild cards.
+-Only the following is currently available
+-
+- <match>* - will match functions that begins with <match>
+- *<match> - will match functions that end with <match>
+- *<match>* - will match functions that have <match> in it
+-
+-Thats all the wild cards that are allowed.
+-
+- <match>*<match> will not work.
+-
+- # echo hrtimer_* > /debug/tracing/set_ftrace_filter
+-
+-Produces:
+-
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- bash-4003 [00] 1480.611794: hrtimer_init <-copy_process
+- bash-4003 [00] 1480.611941: hrtimer_start <-hrtick_set
+- bash-4003 [00] 1480.611956: hrtimer_cancel <-hrtick_clear
+- bash-4003 [00] 1480.611956: hrtimer_try_to_cancel <-hrtimer_cancel
+- <idle>-0 [00] 1480.612019: hrtimer_get_next_event <-get_next_timer_interrupt
+- <idle>-0 [00] 1480.612025: hrtimer_get_next_event <-get_next_timer_interrupt
+- <idle>-0 [00] 1480.612032: hrtimer_get_next_event <-get_next_timer_interrupt
+- <idle>-0 [00] 1480.612037: hrtimer_get_next_event <-get_next_timer_interrupt
+- <idle>-0 [00] 1480.612382: hrtimer_get_next_event <-get_next_timer_interrupt
+-
+-
+-Notice that we lost the sys_nanosleep.
+-
+- # cat /debug/tracing/set_ftrace_filter
+-hrtimer_run_queues
+-hrtimer_run_pending
+-hrtimer_init
+-hrtimer_cancel
+-hrtimer_try_to_cancel
+-hrtimer_forward
+-hrtimer_start
+-hrtimer_reprogram
+-hrtimer_force_reprogram
+-hrtimer_get_next_event
+-hrtimer_interrupt
+-hrtimer_nanosleep
+-hrtimer_wakeup
+-hrtimer_get_remaining
+-hrtimer_get_res
+-hrtimer_init_sleeper
+-
+-
+-This is because the '>' and '>>' act just like they do in bash.
+-To rewrite the filters, use '>'
+-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
+- #
+-
+-Again, now we want to append.
+-
+- # echo sys_nanosleep > /debug/tracing/set_ftrace_filter
+- # cat /debug/tracing/set_ftrace_filter
+-sys_nanosleep
+- # echo hrtimer_* >> /debug/tracing/set_ftrace_filter
+- # cat /debug/tracing/set_ftrace_filter
+-hrtimer_run_queues
+-hrtimer_run_pending
+-hrtimer_init
+-hrtimer_cancel
+-hrtimer_try_to_cancel
+-hrtimer_forward
+-hrtimer_start
+-hrtimer_reprogram
+-hrtimer_force_reprogram
+-hrtimer_get_next_event
+-hrtimer_interrupt
+-sys_nanosleep
+-hrtimer_nanosleep
+-hrtimer_wakeup
+-hrtimer_get_remaining
+-hrtimer_get_res
+-hrtimer_init_sleeper
+-
+-
+-The set_ftrace_notrace prevents those functions from being traced.
+-
+- # echo '*preempt*' '*lock*' > /debug/tracing/set_ftrace_notrace
+-
+-Produces:
+-
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+- bash-4043 [01] 115.281644: finish_task_switch <-schedule
+- bash-4043 [01] 115.281645: hrtick_set <-schedule
+- bash-4043 [01] 115.281645: hrtick_clear <-hrtick_set
+- bash-4043 [01] 115.281646: wait_for_completion <-__stop_machine_run
+- bash-4043 [01] 115.281647: wait_for_common <-wait_for_completion
+- bash-4043 [01] 115.281647: kthread_stop <-stop_machine_run
+- bash-4043 [01] 115.281648: init_waitqueue_head <-kthread_stop
+- bash-4043 [01] 115.281648: wake_up_process <-kthread_stop
+- bash-4043 [01] 115.281649: try_to_wake_up <-wake_up_process
+-
+-We can see that there's no more lock or preempt tracing.
+-
+-ftraced
+--------
+-
+-As mentioned above, when dynamic ftrace is configured in, a kernel
+-thread wakes up once a second and checks to see if there are mcount
+-calls that need to be converted into nops. If there is not, then
+-it simply goes back to sleep. But if there is, it will call
+-kstop_machine to convert the calls to nops.
+-
+-There may be a case that you do not want this added latency.
+-Perhaps you are doing some audio recording and this activity might
+-cause skips in the playback. There is an interface to disable
+-and enable the ftraced kernel thread.
+-
+- # echo 0 > /debug/tracing/ftraced_enabled
+-
+-This will disable the calling of the kstop_machine to update the
+-mcount calls to nops. Remember that there's a large overhead
+-to calling mcount. Without this kernel thread, that overhead will
+-exist.
+-
+-Any write to the ftraced_enabled file will cause the kstop_machine
+-to run if there are recorded calls to mcount. This means that a
+-user can manually perform the updates when they want to by simply
+-echoing a '0' into the ftraced_enabled file.
+-
+-The updates are also done at the beginning of enabling a tracer
+-that uses ftrace function recording.
+-
+-
+-trace_pipe
+-----------
+-
+-The trace_pipe outputs the same as trace, but 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 ftrace > /debug/tracing/current_tracer
+- # cat /debug/tracing/trace_pipe > /tmp/trace.out &
+-[1] 4153
+- # echo 1 > /debug/tracing/tracing_enabled
+- # usleep 1
+- # echo 0 > /debug/tracing/tracing_enabled
+- # cat /debug/tracing/trace
+-# tracer: ftrace
+-#
+-# TASK-PID CPU# TIMESTAMP FUNCTION
+-# | | | | |
+-
+- #
+- # cat /tmp/trace.out
+- bash-4043 [00] 41.267106: finish_task_switch <-schedule
+- bash-4043 [00] 41.267106: hrtick_set <-schedule
+- bash-4043 [00] 41.267107: hrtick_clear <-hrtick_set
+- bash-4043 [00] 41.267108: wait_for_completion <-__stop_machine_run
+- bash-4043 [00] 41.267108: wait_for_common <-wait_for_completion
+- bash-4043 [00] 41.267109: kthread_stop <-stop_machine_run
+- bash-4043 [00] 41.267109: init_waitqueue_head <-kthread_stop
+- bash-4043 [00] 41.267110: wake_up_process <-kthread_stop
+- bash-4043 [00] 41.267110: try_to_wake_up <-wake_up_process
+- bash-4043 [00] 41.267111: select_task_rq_rt <-try_to_wake_up
+-
+-
+-Note, reading the trace_pipe will block until more input is added.
+-By changing the tracer, trace_pipe will issue an EOF. We needed
+-to set the ftrace tracer _before_ cating the trace_pipe file.
+-
+-
+-trace entries
+--------------
+-
+-Having too much or not enough data can be troublesome in diagnosing
+-some issue in the kernel. The file trace_entries is used to modify
+-the size of the internal trace buffers. The numbers 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/trace_entries
+-65620
+-
+-Note, to modify this you must have tracing fulling disabled. To do that,
+-echo "none" into the current_tracer.
+-
+- # echo none > /debug/tracing/current_tracer
+- # echo 100000 > /debug/tracing/trace_entries
+- # cat /debug/tracing/trace_entries
+-100045
+-
+-
+-Notice that we echoed in 100,000 but the size is 100,045. The entries
+-are held by individual pages. It allocates the number of pages it takes
+-to fulfill the request. If more entries may fit on the last page
+-it will add them.
+-
+- # echo 1 > /debug/tracing/trace_entries
+- # cat /debug/tracing/trace_entries
+-85
+-
+-This shows us that 85 entries can fit on a single page.
+-
+-The number of pages that will be allocated is a percentage of available
+-memory. Allocating too much will produces an error.
+-
+- # echo 1000000000000 > /debug/tracing/trace_entries
+--bash: echo: write error: Cannot allocate memory
+- # cat /debug/tracing/trace_entries
+-85
+-
projects / thirdparty / kernel / stable-queue.git / commitdiff
