tracing: Update subbuffer with kilobytes not page order

[linux-2.6-block.git] / Documentation / trace / ftrace.rst

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 231d26ceedb05c138bc088d620490b11970369dd..933e7efb9f1b322ffc96b5a47d26b76401483d6c 100644 (file)
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -203,32 +203,26 @@ 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.
+  buffer_subbuf_size_kb:
+
+       This sets or displays the sub buffer size. 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.
+
+       Note, the buffer_subbuf_size_kb is a way for the user to specify the
+       minimum size of the subbuffer. The kernel may make it bigger due to the
+       implementation details, or simply fail the operation if the kernel can
+       not handle the request.
+
+       Changing the sub buffer size allows for events to be larger than the
+       page size.
+
+       Note: When changing the sub-buffer size, tracing is stopped and any
+       data in the ring buffer and the snapshot buffer will be discarded.
 
   free_buffer: