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

[Masami Hiramatsu <mhiramat@kernel.org>]

Hi Randy,

Thank you for your comments!

On Sat, 18 Jan 2020 10:14:08 -0800
Randy Dunlap <rdunlap@infradead.org> wrote:

> 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.

Oops, OK.

> 
> > +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

OK.

> 
> > +
> > +
> > +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.

Yes, I missed it.

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

OK.

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

OK.

> 
> > +
> > +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]

OK.

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

OK.

> 
> > +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.

Very helpful. Thanks!


-- 
Masami Hiramatsu <mhiramat@kernel.org>