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222 lines
7.1 KiB
222 lines
7.1 KiB
.. 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 <[email protected]> |
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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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