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authorMasami Hiramatsu <mhiramat@kernel.org>2020-09-10 15:39:27 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2020-09-22 04:06:04 +0300
commitfd264ce96c382bc2e36eb1f49ac45c5980650244 (patch)
tree6cba171396e64eea548b421115943c2a40326adc /Documentation/trace
parentba0fbfbb21cd90d51e4f6668ee8397e810818028 (diff)
downloadlinux-fd264ce96c382bc2e36eb1f49ac45c5980650244.tar.xz
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>
Diffstat (limited to 'Documentation/trace')
-rw-r--r--Documentation/trace/boottime-trace.rst14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
index ab3bfd67197c..89b64334929b 100644
--- a/Documentation/trace/boottime-trace.rst
+++ b/Documentation/trace/boottime-trace.rst
@@ -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
========