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| author |   Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-12-19 13:54:27 -0500 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-12-21 11:03:13 -0500 |
| commit | 7c3f48026589b532ebc0d12f939f6be78bd74a58 (patch) | |
| tree | a1a90b6ff47c358cec009666777aad21b1b001fb /Documentation/trace | |
| parent | ring-buffer: Just update the subbuffers when changing their allocation order (diff) | |
| download | wireguard-linux-7c3f48026589b532ebc0d12f939f6be78bd74a58.tar.xz wireguard-linux-7c3f48026589b532ebc0d12f939f6be78bd74a58.zip | |
ring-buffer: Add documentation on the buffer_subbuf_order file
Add to the documentation how to use the buffer_subbuf_order file to change
the size and how it affects what events can be added to the ring buffer.
Link: https://lore.kernel.org/linux-trace-kernel/20231219185631.230636734@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 23572f6697c0..231d26ceedb0 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -203,6 +203,33 @@ of ftrace. Here is a list of some of the key files: This displays the total combined size of all the trace buffers. + buffer_subbuf_order: + + This sets or displays the sub buffer page size order. The ring buffer + is broken up into several same size "sub buffers". An event can not be + bigger than the size of the sub buffer. Normally, the sub buffer is + the size of the architecture's page (4K on x86). The sub buffer also + contains meta data at the start which also limits the size of an event. + That means when the sub buffer is a page size, no event can be larger + than the page size minus the sub buffer meta data. + + The buffer_subbuf_order allows the user to change the size of the sub + buffer. As the sub buffer is a set of pages by the power of 2, thus + the sub buffer total size is defined by the order: + + order size + ---- ---- + 0 PAGE_SIZE + 1 PAGE_SIZE * 2 + 2 PAGE_SIZE * 4 + 3 PAGE_SIZE * 8 + + Changing the order will change the sub buffer size allowing for events + to be larger than the page size. + + Note: When changing the order, tracing is stopped and any data in the + ring buffer and the snapshot buffer will be discarded. + free_buffer: If a process is performing tracing, and the ring buffer should be |