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Diffstat (limited to 'Documentation/trace/ftrace.rst')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 46 |
1 files changed, 20 insertions, 26 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 231d26ceedb0..933e7efb9f1b 100644 --- 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: |