[RFC PATCH v4 22/22] Documentation: tracing: Add boot-time tracing document

Masami Hiramatsu
2019-12-02T10:17:33Z

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/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index db35cee8a00a..ab015e512614 100644
--- a/Documentation/admin-guide/bootconfig.rst
+++ b/Documentation/admin-guide/bootconfig.rst
@@ -1,5 +1,7 @@
.. SPDX-License-Identifier: GPL-2.0

+.. _bootconfig:
+
==================
Boot Configuration
==================
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
+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.
+
+
+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
+
+ftrace.[instance.INSTANCE.]ftrace.notraces
+ This will take an array of NON-tracing function filter rules
+
+
+Ftrace Per-Event Options
+------------------------
+
+These options are setting per-event options.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
+ Enables GROUP:EVENT tracing.
+
+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
+several tracers for different purpose at once. For example, one tracer
+is for tracing functions start with "user\_", and others tracing "kernel\_"
+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".
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index b7891cb1ab4d..47d6b466e308 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -19,6 +19,7 @@ Linux Tracing Technologies
events-msr
mmiotrace
histogram
+ boottime-trace
hwlat_detector
intel_th
stm