From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Andrew Morton <akpm@linux-foundation.org>,
Tzvetomir Stoyanov <tz.stoyanov@gmail.com>,
Vincent Donnefort <vdonnefort@google.com>,
Kent Overstreet <kent.overstreet@gmail.com>
Subject: [PATCH 13/14] ring-buffer: Add documentation on the buffer_subbuf_order file
Date: Sat, 09 Dec 2023 22:54:17 -0500 [thread overview]
Message-ID: <20231210040451.982725347@goodmis.org> (raw)
In-Reply-To: 20231210035404.053677508@goodmis.org
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
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.
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Documentation/trace/ftrace.rst | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
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
--
2.42.0
next prev parent reply other threads:[~2023-12-10 4:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-10 3:54 [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Steven Rostedt
2023-12-10 3:54 ` [PATCH 01/14] ring-buffer: Refactor ring buffer implementation Steven Rostedt
2023-12-10 3:54 ` [PATCH 02/14] ring-buffer: Page size per ring buffer Steven Rostedt
2023-12-10 3:54 ` [PATCH 03/14] ring-buffer: Add interface for configuring trace sub buffer size Steven Rostedt
2023-12-10 3:54 ` [PATCH 04/14] ring-buffer: Set new size of the ring buffer sub page Steven Rostedt
2023-12-10 3:54 ` [PATCH 05/14] ring-buffer: Read and write to ring buffers with custom sub buffer size Steven Rostedt
2023-12-10 3:54 ` [PATCH 06/14] ring-buffer: Clear pages on error in ring_buffer_subbuf_order_set() failure Steven Rostedt
2023-12-10 3:54 ` [PATCH 07/14] ring-buffer: Do no swap cpu buffers if order is different Steven Rostedt
2023-12-10 3:54 ` [PATCH 08/14] ring-buffer: Make sure the spare sub buffer used for reads has same size Steven Rostedt
2023-12-10 3:54 ` [PATCH 09/14] tracing: Update snapshot order along with main buffer order Steven Rostedt
2023-12-10 3:54 ` [PATCH 10/14] tracing: Stop the tracing while changing the ring buffer subbuf size Steven Rostedt
2023-12-10 3:54 ` [PATCH 11/14] ring-buffer: Keep the same size when updating the order Steven Rostedt
2023-12-10 3:54 ` [PATCH 12/14] ring-buffer: Just update the subbuffers when changing their allocation order Steven Rostedt
2023-12-10 3:54 ` Steven Rostedt [this message]
2023-12-10 14:28 ` [PATCH 13/14] ring-buffer: Add documentation on the buffer_subbuf_order file Mathieu Desnoyers
2023-12-10 3:54 ` [PATCH 14/14] ringbuffer/selftest: Add basic selftest to test chaning subbuf order Steven Rostedt
2023-12-10 14:26 ` Mathieu Desnoyers
2023-12-10 15:44 ` Steven Rostedt
2023-12-10 14:17 ` [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Mathieu Desnoyers
2023-12-10 15:38 ` Steven Rostedt
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