1.. SPDX-License-Identifier: GPL-2.0 2 3================= 4Boot-time tracing 5================= 6 7:Author: Masami Hiramatsu <mhiramat@kernel.org> 8 9Overview 10======== 11 12Boot-time tracing allows users to trace boot-time process including 13device initialization with full features of ftrace including per-event 14filter and actions, histograms, kprobe-events and synthetic-events, 15and trace instances. 16Since kernel command line is not enough to control these complex features, 17this uses bootconfig file to describe tracing feature programming. 18 19Options in the Boot Config 20========================== 21 22Here is the list of available options for boot time tracing in 23boot config file [1]_. All options are under "ftrace." or "kernel." 24prefix. See kernel parameters for the options which starts 25with "kernel." prefix [2]_. 26 27.. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>` 28.. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>` 29 30Ftrace Global Options 31--------------------- 32 33Ftrace global options have "kernel." prefix in boot config, which means 34these options are passed as a part of kernel legacy command line. 35 36kernel.tp_printk 37 Output trace-event data on printk buffer too. 38 39kernel.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. 42 43kernel.traceoff_on_warning 44 Stop tracing if WARN_ON() occurs. 45 46kernel.fgraph_max_depth = MAX_DEPTH 47 Set MAX_DEPTH to maximum depth of fgraph tracer. 48 49kernel.fgraph_filters = FILTER[, FILTER2...] 50 Add fgraph tracing function filters. 51 52kernel.fgraph_notraces = FILTER[, FILTER2...] 53 Add fgraph non-tracing function filters. 54 55 56Ftrace Per-instance Options 57--------------------------- 58 59These options can be used for each instance including global ftrace node. 60 61ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]] 62 Enable given ftrace options. 63 64ftrace.[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) 67 68ftrace.[instance.INSTANCE.]trace_clock = CLOCK 69 Set given CLOCK to ftrace's trace_clock. 70 71ftrace.[instance.INSTANCE.]buffer_size = SIZE 72 Configure ftrace buffer size to SIZE. You can use "KB" or "MB" 73 for that SIZE. 74 75ftrace.[instance.INSTANCE.]alloc_snapshot 76 Allocate snapshot buffer. 77 78ftrace.[instance.INSTANCE.]cpumask = CPUMASK 79 Set CPUMASK as trace cpu-mask. 80 81ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]] 82 Enable given events on boot. You can use a wild card in EVENT. 83 84ftrace.[instance.INSTANCE.]tracer = TRACER 85 Set TRACER to current tracer on boot. (e.g. function) 86 87ftrace.[instance.INSTANCE.]ftrace.filters 88 This will take an array of tracing function filter rules. 89 90ftrace.[instance.INSTANCE.]ftrace.notraces 91 This will take an array of NON-tracing function filter rules. 92 93 94Ftrace Per-Event Options 95------------------------ 96 97These options are setting per-event options. 98 99ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable 100 Enable GROUP:EVENT tracing. 101 102ftrace.[instance.INSTANCE.]event.GROUP.enable 103 Enable all event tracing within GROUP. 104 105ftrace.[instance.INSTANCE.]event.enable 106 Enable all event tracing. 107 108ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER 109 Set FILTER rule to the GROUP:EVENT. 110 111ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]] 112 Set ACTIONs to the GROUP:EVENT. 113 114ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]] 115 Defines new kprobe event based on PROBEs. It is able to define 116 multiple probes on one event, but those must have same type of 117 arguments. This option is available only for the event which 118 group name is "kprobes". 119 120ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]] 121 Defines new synthetic event with FIELDs. Each field should be 122 "type varname". 123 124ftrace.[instance.INSTANCE.]event.eprobes.EVENT.probes = PROBE[, PROBE2[...]] 125 Defines new event probe based on PROBEs. This option is available only 126 for the event which group name is "eprobes". 127 128ftrace.[instance.INSTANCE.]event.fprobes.EVENT.probes = PROBE[, PROBE2[...]] 129 Defines new fprobe event based on PROBEs. This option is available only 130 for the event which group name is "fprobes". 131 132ftrace.[instance.INSTANCE.]event.tracepoints.EVENT.probes = PROBE[, PROBE2[...]] 133 Defines new tracepoint probe based on PROBEs. This option is available only 134 for the event which group name is "tracepoints" or "tprobes". 135 136Note that dynamic event definitions can be written under instance node, but 137those are also visible from other instances. So please take care for event 138name conflict. 139 140Ftrace Histogram Options 141------------------------ 142 143Since it is too long to write a histogram action as a string for per-event 144action option, there are tree-style options under per-event 'hist' subkey 145for the histogram actions. For the detail of the each parameter, 146please read the event histogram document (Documentation/trace/histogram.rst) 147 148ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]keys = KEY1[, KEY2[...]] 149 Set histogram key parameters. (Mandatory) 150 The 'N' is a digit string for the multiple histogram. You can omit it 151 if there is one histogram on the event. 152 153ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]values = VAL1[, VAL2[...]] 154 Set histogram value parameters. 155 156ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]sort = SORT1[, SORT2[...]] 157 Set histogram sort parameter options. 158 159ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]size = NR_ENTRIES 160 Set histogram size (number of entries). 161 162ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]name = NAME 163 Set histogram name. 164 165ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]var.VARIABLE = EXPR 166 Define a new VARIABLE by EXPR expression. 167 168ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<pause|continue|clear> 169 Set histogram control parameter. You can set one of them. 170 171ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]event = GROUP.EVENT 172 Set histogram 'onmatch' handler matching event parameter. 173 The 'M' is a digit string for the multiple 'onmatch' handler. You can omit it 174 if there is one 'onmatch' handler on this histogram. 175 176ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]trace = EVENT[, ARG1[...]] 177 Set histogram 'trace' action for 'onmatch'. 178 EVENT must be a synthetic event name, and ARG1... are parameters 179 for that event. Mandatory if 'onmatch.event' option is set. 180 181ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmax.[M.]var = VAR 182 Set histogram 'onmax' handler variable parameter. 183 184ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onchange.[M.]var = VAR 185 Set histogram 'onchange' handler variable parameter. 186 187ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<onmax|onchange>.[M.]save = ARG1[, ARG2[...]] 188 Set histogram 'save' action parameters for 'onmax' or 'onchange' handler. 189 This option or below 'snapshot' option is mandatory if 'onmax.var' or 190 'onchange.var' option is set. 191 192ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<onmax|onchange>.[M.]snapshot 193 Set histogram 'snapshot' action for 'onmax' or 'onchange' handler. 194 This option or above 'save' option is mandatory if 'onmax.var' or 195 'onchange.var' option is set. 196 197ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.filter = FILTER_EXPR 198 Set histogram filter expression. You don't need 'if' in the FILTER_EXPR. 199 200Note that this 'hist' option can conflict with the per-event 'actions' 201option if the 'actions' option has a histogram action. 202 203 204When to Start 205============= 206 207All boot-time tracing options starting with ``ftrace`` will be enabled at the 208end of core_initcall. This means you can trace the events from postcore_initcall. 209Most of the subsystems and architecture dependent drivers will be initialized 210after that (arch_initcall or subsys_initcall). Thus, you can trace those with 211boot-time tracing. 212If you want to trace events before core_initcall, you can use the options 213starting with ``kernel``. Some of them will be enabled earlier than the initcall 214processing (for example, ``kernel.ftrace=function`` and ``kernel.trace_event`` 215will start before the initcall.) 216 217 218Examples 219======== 220 221For example, to add filter and actions for each event, define kprobe 222events, and synthetic events with histogram, write a boot config like 223below:: 224 225 ftrace.event { 226 task.task_newtask { 227 filter = "pid < 128" 228 enable 229 } 230 kprobes.vfs_read { 231 probes = "vfs_read $arg1 $arg2" 232 filter = "common_pid < 200" 233 enable 234 } 235 synthetic.initcall_latency { 236 fields = "unsigned long func", "u64 lat" 237 hist { 238 keys = func.sym, lat 239 values = lat 240 sort = lat 241 } 242 } 243 initcall.initcall_start.hist { 244 keys = func 245 var.ts0 = common_timestamp.usecs 246 } 247 initcall.initcall_finish.hist { 248 keys = func 249 var.lat = common_timestamp.usecs - $ts0 250 onmatch { 251 event = initcall.initcall_start 252 trace = initcall_latency, func, $lat 253 } 254 } 255 } 256 257Also, boot-time tracing supports "instance" node, which allows us to run 258several tracers for different purpose at once. For example, one tracer 259is for tracing functions starting with "user\_", and others tracing 260"kernel\_" functions, you can write boot config as below:: 261 262 ftrace.instance { 263 foo { 264 tracer = "function" 265 ftrace.filters = "user_*" 266 } 267 bar { 268 tracer = "function" 269 ftrace.filters = "kernel_*" 270 } 271 } 272 273The instance node also accepts event nodes so that each instance 274can customize its event tracing. 275 276With the trigger action and kprobes, you can trace function-graph while 277a function is called. For example, this will trace all function calls in 278the pci_proc_init():: 279 280 ftrace { 281 tracing_on = 0 282 tracer = function_graph 283 event.kprobes { 284 start_event { 285 probes = "pci_proc_init" 286 actions = "traceon" 287 } 288 end_event { 289 probes = "pci_proc_init%return" 290 actions = "traceoff" 291 } 292 } 293 } 294 295 296This boot-time tracing also supports ftrace kernel parameters via boot 297config. 298For example, following kernel parameters:: 299 300 trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*" 301 302This can be written in boot config like below:: 303 304 kernel { 305 trace_options = sym-addr 306 trace_event = "initcall:*" 307 tp_printk 308 trace_buf_size = 1M 309 ftrace = function 310 ftrace_filter = "vfs*" 311 } 312 313Note that parameters start with "kernel" prefix instead of "ftrace". 314