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ring-buffer/Documentation: Add documentation on buffer_percent file

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When the buffer_percent file was added to the kernel, the documentation
should have been updated to document what that file does.

Acked-by: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Fixes: 03329f9939 ("tracing: Add tracefs file buffer_percentage")
Signed-off-by: "Steven Rostedt (Google)" <rostedt@goodmis.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231229122402.537eb252@gandalf.local.home
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Steven Rostedt (Google) 2023-12-29 12:24:02 -05:00 committed by Jonathan Corbet
parent d78bcf646c
commit 4b2df884b8
1 changed files with 15 additions and 0 deletions
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15
Documentation/trace/ftrace.rst
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@ -180,6 +180,21 @@ of ftrace. Here is a list of some of the key files:
Only active when the file contains a number greater than 0.
(in microseconds)
buffer_percent:
This is the watermark for how much the ring buffer needs to be filled
before a waiter is woken up. That is, if an application calls a
blocking read syscall on one of the per_cpu trace_pipe_raw files, it
will block until the given amount of data specified by buffer_percent
is in the ring buffer before it wakes the reader up. This also
controls how the splice system calls are blocked on this file::
0 - means to wake up as soon as there is any data in the ring buffer.
50 - means to wake up when roughly half of the ring buffer sub-buffers
are full.
100 - means to block until the ring buffer is totally full and is
about to start overwriting the older data.
buffer_size_kb:
This sets or displays the number of kilobytes each CPU