Re: [PATCH v6 22/22] Documentation: tracing: Add boot-time tracing document

Randy Dunlap
2020-01-18T18:14:48Z

Hi,

Here are a few editorial comments for you...

On 1/10/20 8:07 AM, Masami Hiramatsu wrote:
> Add a documentation about boot-time tracing options in
> boot config.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> Documentation/admin-guide/bootconfig.rst | 2
> Documentation/trace/boottime-trace.rst | 184 ++++++++++++++++++++++++++++++
> Documentation/trace/index.rst | 1
> 3 files changed, 187 insertions(+)
> create mode 100644 Documentation/trace/boottime-trace.rst
>

> diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
> new file mode 100644
> index 000000000000..1d10fdebf1b2
> --- /dev/null
> +++ b/Documentation/trace/boottime-trace.rst
> @@ -0,0 +1,184 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=================
> +Boot-time tracing
> +=================
> +
> +:Author: Masami Hiramatsu <mhiramat@kernel.org>
> +
> +Overview
> +========
> +
> +Boot-time tracing allows users to trace boot-time process including
> +device initialization with full features of ftrace including per-event
> +filter and actions, histograms, kprobe-events and synthetic-events,
> +and trace instances.
> +Since kernel cmdline is not enough to control these complex features,
> +this uses bootconfig file to describe tracing feature programming.
> +
> +Options in the Boot Config
> +==========================
> +
> +Here is the list of available options list for boot time tracing in
> +boot config file [1]_. All options are under "ftrace." or "kernel."
> +refix. See kernel parameters for the options which starts

prefix.

> +with "kernel." prefix [2]_.
> +
> +.. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>`
> +.. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>`
> +
> +Ftrace Global Options
> +---------------------
> +
> +Ftrace global options have "kernel." prefix in boot config, which means
> +these options are passed as a part of kernel legacy command line.
> +
> +kernel.tp_printk
> + Output trace-event data on printk buffer too.
> +
> +kernel.dump_on_oops [= MODE]
> + Dump ftrace on Oops. If MODE = 1 or omitted, dump trace buffer
> + on all CPUs. If MODE = 2, dump a buffer on a CPU which kicks Oops.
> +
> +kernel.traceoff_on_warning
> + Stop tracing if WARN_ON() occurs.
> +
> +kernel.fgraph_max_depth = MAX_DEPTH
> + Set MAX_DEPTH to maximum depth of fgraph tracer.
> +
> +kernel.fgraph_filters = FILTER[, FILTER2...]
> + Add fgraph tracing function filters.
> +
> +kernel.fgraph_notraces = FILTER[, FILTER2...]
> + Add fgraph non tracing function filters.

non-tracing

> +
> +
> +Ftrace Per-instance Options
> +---------------------------
> +
> +These options can be used for each instance including global ftrace node.
> +
> +ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]]
> + Enable given ftrace options.
> +
> +ftrace.[instance.INSTANCE.]trace_clock = CLOCK
> + Set given CLOCK to ftrace's trace_clock.
> +
> +ftrace.[instance.INSTANCE.]buffer_size = SIZE
> + Configure ftrace buffer size to SIZE. You can use "KB" or "MB"
> + for that SIZE.
> +
> +ftrace.[instance.INSTANCE.]alloc_snapshot
> + Allocate snapshot buffer.
> +
> +ftrace.[instance.INSTANCE.]cpumask = CPUMASK
> + Set CPUMASK as trace cpu-mask.
> +
> +ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]]
> + Enable given events on boot. You can use a wild card in EVENT.
> +
> +ftrace.[instance.INSTANCE.]tracer = TRACER
> + Set TRACER to current tracer on boot. (e.g. function)
> +
> +ftrace.[instance.INSTANCE.]ftrace.filters
> + This will take an array of tracing function filter rules

end with '.' as above descriptions.

> +
> +ftrace.[instance.INSTANCE.]ftrace.notraces
> + This will take an array of NON-tracing function filter rules

ditto

> +
> +
> +Ftrace Per-Event Options
> +------------------------
> +
> +These options are setting per-event options.
> +
> +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
> + Enables GROUP:EVENT tracing.

Enable

> +
> +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
> + Set FILTER rule to the GROUP:EVENT.
> +
> +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]]
> + Set ACTIONs to the GROUP:EVENT.
> +
> +ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]]
> + Defines new kprobe event based on PROBEs. It is able to define
> + multiple probes on one event, but those must have same type of
> + arguments. This option is available only for the event which
> + group name is "kprobes".
> +
> +ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]]
> + Defines new synthetic event with FIELDs. Each field should be
> + "type varname".
> +
> +Note that kprobe and synthetic event definitions can be written under
> +instance node, but those are also visible from other instances. So please
> +take care for event name conflict.
> +
> +
> +Examples
> +========
> +
> +For example, to add filter and actions for each event, define kprobe
> +events, and synthetic events with histogram, write a boot config like
> +below::
> +
> + ftrace.event {
> + task.task_newtask {
> + filter = "pid < 128"
> + enable
> + }
> + kprobes.vfs_read {
> + probes = "vfs_read $arg1 $arg2"
> + filter = "common_pid < 200"
> + enable
> + }
> + synthetic.initcall_latency {
> + fields = "unsigned long func", "u64 lat"
> + actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
> + }
> + initcall.initcall_start {
> + actions = "hist:keys=func:ts0=common_timestamp.usecs"
> + }
> + initcall.initcall_finish {
> + actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
> + }
> + }
> +
> +Also, boottime tracing supports "instance" node, which allows us to run

boot-time [for consistency]

> +several tracers for different purpose at once. For example, one tracer
> +is for tracing functions start with "user\_", and others tracing "kernel\_"

starting

> +functions, you can write boot config as below::
> +
> + ftrace.instance {
> + foo {
> + tracer = "function"
> + ftrace.filters = "user_*"
> + }
> + bar {
> + tracer = "function"
> + ftrace.filters = "kernel_*"
> + }
> + }
> +
> +The instance node also accepts event nodes so that each instance
> +can customize its event tracing.
> +
> +This boot-time tracing also supports ftrace kernel parameters via boot
> +config.
> +For example, following kernel parameters::
> +
> + trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*"
> +
> +This can be written in boot config like below::
> +
> + kernel {
> + trace_options = sym-addr
> + trace_event = "initcall:*"
> + tp_printk
> + trace_buf_size = 1M
> + ftrace = function
> + ftrace_filter = "vfs*"
> + }
> +
> +Note that parameters start with "kernel" prefix instead of "ftrace".

HTH.
--
~Randy