1 .. SPDX-License-Identifier: GPL-2.0
7 :Author: Masami Hiramatsu <mhiramat@kernel.org>
12 Boot-time tracing allows users to trace boot-time process including
13 device initialization with full features of ftrace including per-event
14 filter and actions, histograms, kprobe-events and synthetic-events,
16 Since kernel command line is not enough to control these complex features,
17 this uses bootconfig file to describe tracing feature programming.
19 Options in the Boot Config
20 ==========================
22 Here is the list of available options list for boot time tracing in
23 boot config file [1]_. All options are under "ftrace." or "kernel."
24 prefix. See kernel parameters for the options which starts
25 with "kernel." prefix [2]_.
27 .. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>`
28 .. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>`
33 Ftrace global options have "kernel." prefix in boot config, which means
34 these options are passed as a part of kernel legacy command line.
37 Output trace-event data on printk buffer too.
39 kernel.dump_on_oops [= MODE]
40 Dump ftrace on Oops. If MODE = 1 or omitted, dump trace buffer
41 on all CPUs. If MODE = 2, dump a buffer on a CPU which kicks Oops.
43 kernel.traceoff_on_warning
44 Stop tracing if WARN_ON() occurs.
46 kernel.fgraph_max_depth = MAX_DEPTH
47 Set MAX_DEPTH to maximum depth of fgraph tracer.
49 kernel.fgraph_filters = FILTER[, FILTER2...]
50 Add fgraph tracing function filters.
52 kernel.fgraph_notraces = FILTER[, FILTER2...]
53 Add fgraph non-tracing function filters.
56 Ftrace Per-instance Options
57 ---------------------------
59 These options can be used for each instance including global ftrace node.
61 ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]]
62 Enable given ftrace options.
64 ftrace.[instance.INSTANCE.]trace_clock = CLOCK
65 Set given CLOCK to ftrace's trace_clock.
67 ftrace.[instance.INSTANCE.]buffer_size = SIZE
68 Configure ftrace buffer size to SIZE. You can use "KB" or "MB"
71 ftrace.[instance.INSTANCE.]alloc_snapshot
72 Allocate snapshot buffer.
74 ftrace.[instance.INSTANCE.]cpumask = CPUMASK
75 Set CPUMASK as trace cpu-mask.
77 ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]]
78 Enable given events on boot. You can use a wild card in EVENT.
80 ftrace.[instance.INSTANCE.]tracer = TRACER
81 Set TRACER to current tracer on boot. (e.g. function)
83 ftrace.[instance.INSTANCE.]ftrace.filters
84 This will take an array of tracing function filter rules.
86 ftrace.[instance.INSTANCE.]ftrace.notraces
87 This will take an array of NON-tracing function filter rules.
90 Ftrace Per-Event Options
91 ------------------------
93 These options are setting per-event options.
95 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
96 Enable GROUP:EVENT tracing.
98 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
99 Set FILTER rule to the GROUP:EVENT.
101 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]]
102 Set ACTIONs to the GROUP:EVENT.
104 ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]]
105 Defines new kprobe event based on PROBEs. It is able to define
106 multiple probes on one event, but those must have same type of
107 arguments. This option is available only for the event which
108 group name is "kprobes".
110 ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]]
111 Defines new synthetic event with FIELDs. Each field should be
114 Note that kprobe and synthetic event definitions can be written under
115 instance node, but those are also visible from other instances. So please
116 take care for event name conflict.
122 For example, to add filter and actions for each event, define kprobe
123 events, and synthetic events with histogram, write a boot config like
132 probes = "vfs_read $arg1 $arg2"
133 filter = "common_pid < 200"
136 synthetic.initcall_latency {
137 fields = "unsigned long func", "u64 lat"
138 actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
140 initcall.initcall_start {
141 actions = "hist:keys=func:ts0=common_timestamp.usecs"
143 initcall.initcall_finish {
144 actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
148 Also, boot-time tracing supports "instance" node, which allows us to run
149 several tracers for different purpose at once. For example, one tracer
150 is for tracing functions starting with "user\_", and others tracing
151 "kernel\_" functions, you can write boot config as below::
156 ftrace.filters = "user_*"
160 ftrace.filters = "kernel_*"
164 The instance node also accepts event nodes so that each instance
165 can customize its event tracing.
167 This boot-time tracing also supports ftrace kernel parameters via boot
169 For example, following kernel parameters::
171 trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*"
173 This can be written in boot config like below::
176 trace_options = sym-addr
177 trace_event = "initcall:*"
181 ftrace_filter = "vfs*"
184 Note that parameters start with "kernel" prefix instead of "ftrace".