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-rw-r--r--Documentation/trace/ftrace.rst18
1 files changed, 12 insertions, 6 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index d2b5657ed33e..ff658e27d25b 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -95,7 +95,8 @@ of ftrace. Here is a list of some of the key files:
current_tracer:
This is used to set or display the current tracer
- that is configured.
+ that is configured. Changing the current tracer clears
+ the ring buffer content as well as the "snapshot" buffer.
available_tracers:
@@ -126,7 +127,8 @@ of ftrace. Here is a list of some of the key files:
This file holds the output of the trace in a human
readable format (described below). Note, tracing is temporarily
disabled when the file is open for reading. Once all readers
- are closed, tracing is re-enabled.
+ are closed, tracing is re-enabled. Opening this file for
+ writing with the O_TRUNC flag clears the ring buffer content.
trace_pipe:
@@ -185,7 +187,8 @@ of ftrace. Here is a list of some of the key files:
CPU buffer and not total size of all buffers. The
trace buffers are allocated in pages (blocks of memory
that the kernel uses for allocation, usually 4 KB in size).
- If the last page allocated has room for more bytes
+ A few extra pages may be allocated to accommodate buffer management
+ meta-data. If the last page allocated has room for more bytes
than requested, the rest of the page will be used,
making the actual allocation bigger than requested or shown.
( Note, the size may not be a multiple of the page size
@@ -235,7 +238,7 @@ of ftrace. Here is a list of some of the key files:
This interface also allows for commands to be used. See the
"Filter commands" section for more details.
- As a speed up, since processing strings can't be quite expensive
+ As a speed up, since processing strings can be quite expensive
and requires a check of all functions registered to tracing, instead
an index can be written into this file. A number (starting with "1")
written will instead select the same corresponding at the line position
@@ -382,7 +385,7 @@ of ftrace. Here is a list of some of the key files:
By default, 128 comms are saved (see "saved_cmdlines" above). To
increase or decrease the amount of comms that are cached, echo
- in a the number of comms to cache, into this file.
+ the number of comms to cache into this file.
saved_tgids:
@@ -490,6 +493,9 @@ of ftrace. Here is a list of some of the key files:
# echo global > trace_clock
+ Setting a clock clears the ring buffer content as well as the
+ "snapshot" buffer.
+
trace_marker:
This is a very useful file for synchronizing user space
@@ -3324,7 +3330,7 @@ directories after it is created.
As you can see, the new directory looks similar to the tracing directory
itself. In fact, it is very similar, except that the buffer and
-events are agnostic from the main director, or from any other
+events are agnostic from the main directory, or from any other
instances that are created.
The files in the new directory work just like the files with the