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.]tracing_on = 0|1
65 Enable/Disable tracing on this instance when starting boot-time tracing.
66 (you can enable it by the "traceon" event trigger action)
68 ftrace.[instance.INSTANCE.]trace_clock = CLOCK
69 Set given CLOCK to ftrace's trace_clock.
71 ftrace.[instance.INSTANCE.]buffer_size = SIZE
72 Configure ftrace buffer size to SIZE. You can use "KB" or "MB"
75 ftrace.[instance.INSTANCE.]alloc_snapshot
76 Allocate snapshot buffer.
78 ftrace.[instance.INSTANCE.]cpumask = CPUMASK
79 Set CPUMASK as trace cpu-mask.
81 ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]]
82 Enable given events on boot. You can use a wild card in EVENT.
84 ftrace.[instance.INSTANCE.]tracer = TRACER
85 Set TRACER to current tracer on boot. (e.g. function)
87 ftrace.[instance.INSTANCE.]ftrace.filters
88 This will take an array of tracing function filter rules.
90 ftrace.[instance.INSTANCE.]ftrace.notraces
91 This will take an array of NON-tracing function filter rules.
94 Ftrace Per-Event Options
95 ------------------------
97 These options are setting per-event options.
99 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
100 Enable GROUP:EVENT tracing.
102 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
103 Set FILTER rule to the GROUP:EVENT.
105 ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]]
106 Set ACTIONs to the GROUP:EVENT.
108 ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]]
109 Defines new kprobe event based on PROBEs. It is able to define
110 multiple probes on one event, but those must have same type of
111 arguments. This option is available only for the event which
112 group name is "kprobes".
114 ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]]
115 Defines new synthetic event with FIELDs. Each field should be
118 Note that kprobe and synthetic event definitions can be written under
119 instance node, but those are also visible from other instances. So please
120 take care for event name conflict.
126 For example, to add filter and actions for each event, define kprobe
127 events, and synthetic events with histogram, write a boot config like
136 probes = "vfs_read $arg1 $arg2"
137 filter = "common_pid < 200"
140 synthetic.initcall_latency {
141 fields = "unsigned long func", "u64 lat"
142 actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
144 initcall.initcall_start {
145 actions = "hist:keys=func:ts0=common_timestamp.usecs"
147 initcall.initcall_finish {
148 actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
152 Also, boot-time tracing supports "instance" node, which allows us to run
153 several tracers for different purpose at once. For example, one tracer
154 is for tracing functions starting with "user\_", and others tracing
155 "kernel\_" functions, you can write boot config as below::
160 ftrace.filters = "user_*"
164 ftrace.filters = "kernel_*"
168 The instance node also accepts event nodes so that each instance
169 can customize its event tracing.
171 This boot-time tracing also supports ftrace kernel parameters via boot
173 For example, following kernel parameters::
175 trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*"
177 This can be written in boot config like below::
180 trace_options = sym-addr
181 trace_event = "initcall:*"
185 ftrace_filter = "vfs*"
188 Note that parameters start with "kernel" prefix instead of "ftrace".