223 lines
7.1 KiB
ReStructuredText
223 lines
7.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=================
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Boot-time tracing
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=================
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:Author: Masami Hiramatsu <mhiramat@kernel.org>
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Overview
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========
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Boot-time tracing allows users to trace boot-time process including
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device initialization with full features of ftrace including per-event
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filter and actions, histograms, kprobe-events and synthetic-events,
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and trace instances.
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Since kernel command line is not enough to control these complex features,
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this uses bootconfig file to describe tracing feature programming.
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Options in the Boot Config
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==========================
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Here is the list of available options list for boot time tracing in
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boot config file [1]_. All options are under "ftrace." or "kernel."
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prefix. See kernel parameters for the options which starts
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with "kernel." prefix [2]_.
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.. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>`
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.. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>`
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Ftrace Global Options
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---------------------
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Ftrace global options have "kernel." prefix in boot config, which means
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these options are passed as a part of kernel legacy command line.
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kernel.tp_printk
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Output trace-event data on printk buffer too.
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kernel.dump_on_oops [= MODE]
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Dump ftrace on Oops. If MODE = 1 or omitted, dump trace buffer
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on all CPUs. If MODE = 2, dump a buffer on a CPU which kicks Oops.
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kernel.traceoff_on_warning
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Stop tracing if WARN_ON() occurs.
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kernel.fgraph_max_depth = MAX_DEPTH
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Set MAX_DEPTH to maximum depth of fgraph tracer.
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kernel.fgraph_filters = FILTER[, FILTER2...]
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Add fgraph tracing function filters.
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kernel.fgraph_notraces = FILTER[, FILTER2...]
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Add fgraph non-tracing function filters.
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Ftrace Per-instance Options
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---------------------------
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These options can be used for each instance including global ftrace node.
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ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]]
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Enable given ftrace options.
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ftrace.[instance.INSTANCE.]tracing_on = 0|1
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Enable/Disable tracing on this instance when starting boot-time tracing.
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(you can enable it by the "traceon" event trigger action)
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ftrace.[instance.INSTANCE.]trace_clock = CLOCK
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Set given CLOCK to ftrace's trace_clock.
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ftrace.[instance.INSTANCE.]buffer_size = SIZE
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Configure ftrace buffer size to SIZE. You can use "KB" or "MB"
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for that SIZE.
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ftrace.[instance.INSTANCE.]alloc_snapshot
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Allocate snapshot buffer.
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ftrace.[instance.INSTANCE.]cpumask = CPUMASK
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Set CPUMASK as trace cpu-mask.
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ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]]
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Enable given events on boot. You can use a wild card in EVENT.
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ftrace.[instance.INSTANCE.]tracer = TRACER
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Set TRACER to current tracer on boot. (e.g. function)
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ftrace.[instance.INSTANCE.]ftrace.filters
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This will take an array of tracing function filter rules.
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ftrace.[instance.INSTANCE.]ftrace.notraces
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This will take an array of NON-tracing function filter rules.
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Ftrace Per-Event Options
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------------------------
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These options are setting per-event options.
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ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
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Enable GROUP:EVENT tracing.
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ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
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Set FILTER rule to the GROUP:EVENT.
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ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]]
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Set ACTIONs to the GROUP:EVENT.
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ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]]
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Defines new kprobe event based on PROBEs. It is able to define
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multiple probes on one event, but those must have same type of
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arguments. This option is available only for the event which
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group name is "kprobes".
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ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]]
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Defines new synthetic event with FIELDs. Each field should be
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"type varname".
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Note that kprobe and synthetic event definitions can be written under
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instance node, but those are also visible from other instances. So please
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take care for event name conflict.
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When to Start
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=============
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All boot-time tracing options starting with ``ftrace`` will be enabled at the
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end of core_initcall. This means you can trace the events from postcore_initcall.
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Most of the subsystems and architecture dependent drivers will be initialized
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after that (arch_initcall or subsys_initcall). Thus, you can trace those with
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boot-time tracing.
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If you want to trace events before core_initcall, you can use the options
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starting with ``kernel``. Some of them will be enabled eariler than the initcall
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processing (for example,. ``kernel.ftrace=function`` and ``kernel.trace_event``
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will start before the initcall.)
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Examples
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========
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For example, to add filter and actions for each event, define kprobe
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events, and synthetic events with histogram, write a boot config like
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below::
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ftrace.event {
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task.task_newtask {
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filter = "pid < 128"
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enable
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}
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kprobes.vfs_read {
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probes = "vfs_read $arg1 $arg2"
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filter = "common_pid < 200"
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enable
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}
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synthetic.initcall_latency {
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fields = "unsigned long func", "u64 lat"
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actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
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}
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initcall.initcall_start {
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actions = "hist:keys=func:ts0=common_timestamp.usecs"
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}
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initcall.initcall_finish {
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actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
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}
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}
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Also, boot-time tracing supports "instance" node, which allows us to run
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several tracers for different purpose at once. For example, one tracer
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is for tracing functions starting with "user\_", and others tracing
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"kernel\_" functions, you can write boot config as below::
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ftrace.instance {
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foo {
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tracer = "function"
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ftrace.filters = "user_*"
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}
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bar {
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tracer = "function"
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ftrace.filters = "kernel_*"
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}
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}
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The instance node also accepts event nodes so that each instance
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can customize its event tracing.
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With the trigger action and kprobes, you can trace function-graph while
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a function is called. For example, this will trace all function calls in
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the pci_proc_init()::
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ftrace {
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tracing_on = 0
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tracer = function_graph
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event.kprobes {
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start_event {
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probes = "pci_proc_init"
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actions = "traceon"
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}
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end_event {
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probes = "pci_proc_init%return"
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actions = "traceoff"
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}
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}
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}
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This boot-time tracing also supports ftrace kernel parameters via boot
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config.
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For example, following kernel parameters::
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trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*"
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This can be written in boot config like below::
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kernel {
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trace_options = sym-addr
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trace_event = "initcall:*"
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tp_printk
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trace_buf_size = 1M
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ftrace = function
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ftrace_filter = "vfs*"
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}
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Note that parameters start with "kernel" prefix instead of "ftrace".
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