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-rw-r--r--Documentation/trace/ftrace.rst38
1 files changed, 37 insertions, 1 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 23572f6697..7e7b8ec179 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -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
@@ -203,6 +218,27 @@ 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_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:
If a process is performing tracing, and the ring buffer should be
@@ -2574,7 +2610,7 @@ want, depending on your needs.
- The cpu number on which the function executed is default
enabled. It is sometimes better to only trace one cpu (see
- tracing_cpu_mask file) or you might sometimes see unordered
+ tracing_cpumask file) or you might sometimes see unordered
function calls while cpu tracing switch.
- hide: echo nofuncgraph-cpu > trace_options