tracing: Update subbuffer with kilobytes not page order

Using page order for deciding what the size of the ring buffer sub buffers
are is exposing a bit too much of the implementation. Although the sub
buffers are only allocated in orders of pages, allow the user to specify
the minimum size of each sub-buffer via kilobytes like they can with the
buffer size itself.

If the user specifies 3 via:

  echo 3 > buffer_subbuf_size_kb

Then the sub-buffer size will round up to 4kb (on a 4kb page size system).

If they specify:

  echo 6 > buffer_subbuf_size_kb

The sub-buffer size will become 8kb.

and so on.

Link: https://lore.kernel.org/linux-trace-kernel/20231219185631.809766769@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>

1 files changed, 9 insertions, 9 deletions

diff --git a/tools/testing/selftests/ftrace/test.d/00basic/ringbuffer_order.tc b/tools/testing/selftests/ftrace/test.d/00basic/ringbuffer_subbuf_size.tc
index ecbcc810e6c1..d44d09a33a74 100644
--- a/tools/testing/selftests/ftrace/test.d/00basic/ringbuffer_order.tc
+++ b/tools/testing/selftests/ftrace/test.d/00basic/ringbuffer_subbuf_size.tc
@@ -1,7 +1,7 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
-# description: Change the ringbuffer sub-buffer order
-# requires: buffer_subbuf_order
+# description: Change the ringbuffer sub-buffer size
+# requires: buffer_subbuf_size_kb
 # flags: instance
 
 get_buffer_data_size() {
@@ -52,8 +52,8 @@ write_buffer() {
 }
 
 test_buffer() {
-	orde=$1
-	page_size=$((4096<<order))
+	size_kb=$1
+	page_size=$((size_kb*1024))
 
 	size=`get_buffer_data_size`
 
@@ -82,14 +82,14 @@ test_buffer() {
 	fi
 }
 
-ORIG=`cat buffer_subbuf_order`
+ORIG=`cat buffer_subbuf_size_kb`
 
-# Could test bigger orders than 3, but then creating the string
+# Could test bigger sizes than 32K, but then creating the string
 # to write into the ring buffer takes too long
-for a in 0 1 2 3 ; do
-	echo $a > buffer_subbuf_order
+for a in 4 8 16 32 ; do
+	echo $a > buffer_subbuf_size_kb
 	test_buffer $a
 done
 
-echo $ORIG > buffer_subbuf_order
+echo $ORIG > buffer_subbuf_size_kb