Documentation/trace/ftrace.rst

21 Ftrace is an internal tracer designed to help out developers and
26 Although ftrace is typically considered the function tracer, it
100 	This is used to set or display the current tracer
101 	that is configured. Changing the current tracer clears
115 	the tracer or 1 to enable it. Note, this only disables
134         (no tracer running, or tracing_on is zero), it will produce
149 	"trace" file is static, and if the tracer is not
157 	files. Options also exist to modify how a tracer
260 	Have the function tracer only trace the threads whose PID are
266 	traced by the function tracer as well. This option will also
271         Have the function tracer ignore threads whose PID are listed in
277 	traced by the function tracer as well. This option will also
310 	tracer to only trace these functions and the functions that
368 	tracer, or if configured, the function graph tracer. It will
370 	and if the function graph tracer was configured, it will also keep
390 	Used with the function graph tracer. This is the max depth
436 	When the stack tracer is activated, this will display the
443 	that was encountered when the stack tracer is activated.
449 	functions the stack tracer will check.
726 	Function call tracer to trace all kernel functions.
730 	Similar to the function tracer except that the
731 	function tracer probes the functions on their entry
732 	whereas the function graph tracer traces on both entry
739 	The block tracer. The tracer used by the blktrace user
744 	The Hardware Latency tracer is used to detect if the hardware
755 	happens automatically when the tracer is selected.
789 	A special tracer that is used to trace binary module.
796 	This tracer can be configured when tracing likely/unlikely
803 	This is the "trace nothing" tracer. To remove all
839 Examples of using the tracer
851   # tracer: function
874 A header is printed with the tracer name that is represented by
875 the trace. In this case the tracer is "function". Then it shows the
895   # tracer: irqsoff
931 This shows that the current tracer is "irqsoff" tracing the time
1166 	When any event or tracer is enabled, a hook is enabled
1174 	When any event or tracer is enabled, a hook is enabled
1194 		# tracer: function
1222 	functions. This keeps the overhead of the tracer down
1243 	Enable branch tracing with the tracer. This enables branch
1244 	tracer along with the currently set tracer. Enabling this
1245 	with the "nop" tracer is the same as just enabling the
1246 	"branch" tracer.
1249        file when the tracer is active. They always appear in the
1253 Here are the per tracer options:
1255 Options for function tracer:
1265 Options for function_graph tracer:
1267  Since the function_graph tracer has a slightly different output
1317 	When running function graph tracer, to include
1323 	When running function profiler with function graph tracer,
1329 Options for blk tracer:
1344 The irqsoff tracer tracks the time for which interrupts are
1345 disabled. When a new maximum latency is hit, the tracer saves
1361   # tracer: irqsoff
1412   # tracer: irqsoff
1490   # tracer: irqsoff
1546 The preemptoff tracer traces the places that disable preemption.
1547 Like the irqsoff tracer, it records the maximum latency for
1548 which preemption was disabled. The control of preemptoff tracer
1549 is much like the irqsoff tracer.
1560   # tracer: preemptoff
1598   # tracer: preemptoff
1687 The irqsoff tracer will record the total length of
1691 The preemptoff tracer will record the total length of
1698 tracer.
1712   # tracer: preemptirqsoff
1765   # tracer: preemptirqsoff
1881   # tracer: wakeup
1903 The tracer only traces the highest priority task in the system
1928 work well with Real-Time tasks.  The wakeup_rt tracer was designed
1930 not recorded because the tracer only records one worst case and
1933 tracer for a while to see that effect).
1935 Since this tracer only deals with RT tasks, we will run this
1948   # tracer: wakeup
1950   # tracer: wakeup_rt
1999   # tracer: wakeup_rt
2125   # tracer: wakeup_rt
2159 The hardware latency detector is executed by enabling the "hwlat" tracer.
2161 NOTE, this tracer will affect the performance of the system as it will
2168   # tracer: hwlat
2232 	Note, when hwlat tracer is finished (another tracer is
2255 This tracer is the function tracer. Enabling the function tracer
2257 ftrace_enabled is set; otherwise this tracer is a nop.
2267   # tracer: function
2289 Note: function tracer uses ring buffers to store the above
2325   # tracer: function
2337   # tracer: function
2450 function graph tracer
2453 This tracer is similar to the function tracer except that it
2456 task_struct. On function entry the tracer overwrites the return
2467 This tracer is useful in several situations:
2484   # tracer: function_graph
2592     # tracer: function_graph
2676 You might find other useful features for this tracer in the
2775   # tracer: function
2822   # tracer: function
2911   # tracer: function
2970 Dynamic ftrace with the function graph tracer
2974 function tracer and the function-graph-tracer, there are some
2975 special features only available in the function-graph tracer.
3035 function tracer. By default it is enabled (when function tracing is
3193   # tracer: function
3325   # tracer: nop
3342   # tracer: nop
3358 If you try to use this snapshot feature when current tracer is
3397 Notice that none of the function tracer files are there, nor is
3458   # tracer: nop
3507 a function tracer, it makes it convenient to check the stack size
3508 at every function call. This is enabled via the stack tracer.
3550 are not tested by the stack tracer when -mfentry is used.