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Documentation: tracing: Add the startup timing of boot-time tracing

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Add the note about when to start the boot-time tracing.
This will be needed for the people who wants to trace
earlier boot sequence.

Link: https://lkml.kernel.org/r/159974156678.478751.10215894815285734481.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu 2020-09-10 21:39:27 +09:00 committed by Steven Rostedt (VMware)
parent ba0fbfbb21
commit fd264ce96c
1 changed files with 14 additions and 0 deletions
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Documentation/trace/boottime-trace.rst
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@ -120,6 +120,20 @@ instance node, but those are also visible from other instances. So please
take care for event name conflict.
When to Start
=============
All boot-time tracing options starting with ``ftrace`` will be enabled at the
end of core_initcall. This means you can trace the events from postcore_initcall.
Most of the subsystems and architecture dependent drivers will be initialized
after that (arch_initcall or subsys_initcall). Thus, you can trace those with
boot-time tracing.
If you want to trace events before core_initcall, you can use the options
starting with ``kernel``. Some of them will be enabled eariler than the initcall
processing (for example,. ``kernel.ftrace=function`` and ``kernel.trace_event``
will start before the initcall.)
Examples
========