Boot-time tracing¶

Author:	Masami Hiramatsu <mhiramat@kernel.org>

Overview¶

Boot-time tracing allows users to trace boot-time process includingdevice initialization with full features of ftrace including per-eventfilter and actions, histograms, kprobe-events and synthetic-events,and trace instances.Since kernel command line 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 inboot config file[1]. All options are under “ftrace.” or “kernel.”prefix. See kernel parameters for the options which startswith “kernel.” prefix[2].

[1]	SeeDocumentation/admin-guide/bootconfig.rst

[2]	SeeDocumentation/admin-guide/kernel-parameters.rst

Ftrace Global Options¶

Ftrace global options have “kernel.” prefix in boot config, which meansthese 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 bufferon 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: Enable 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 definemultiple probes on one event, but those must have same type ofarguments. This option is available only for the event whichgroup 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 underinstance node, but those are also visible from other instances. So pleasetake care for event name conflict.

Examples¶

For example, to add filter and actions for each event, define kprobeevents, and synthetic events with histogram, write a boot config likebelow:

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, boot-time tracing supports “instance” node, which allows us to runseveral tracers for different purpose at once. For example, one traceris for tracing functions starting 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 instancecan customize its event tracing.

This boot-time tracing also supports ftrace kernel parameters via bootconfig.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”.

Movatterモバイル変換