Documentation: tracing: Add the startup timing of boot-time tracing
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>
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@ -120,6 +120,20 @@ instance node, but those are also visible from other instances. So please
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take care for event name conflict.
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When to Start
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=============
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All boot-time tracing options starting with ``ftrace`` will be enabled at the
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end of core_initcall. This means you can trace the events from postcore_initcall.
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Most of the subsystems and architecture dependent drivers will be initialized
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after that (arch_initcall or subsys_initcall). Thus, you can trace those with
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boot-time tracing.
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If you want to trace events before core_initcall, you can use the options
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starting with ``kernel``. Some of them will be enabled eariler than the initcall
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processing (for example,. ``kernel.ftrace=function`` and ``kernel.trace_event``
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will start before the initcall.)
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Examples
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========
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