ftrace: show buffer size in kilobytes
Impact: change the units of buffer_size_kb to kilobytes
This patch changes the units of the buffer_size_kb file to kilobytes.
Reading and writing to the file uses kilobytes as units. To help
users to know what units are used, the output of the file now
looks like:
# cat /debug/tracing/buffer_size_kb
1408
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
index a1b5877..6d3fe4c 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -94,10 +94,10 @@
only be recorded if the latency is greater than
the value in this file. (in microseconds)
- buffer_size_kb: This sets or displays the number of bytes each CPU
+ buffer_size_kb: This sets or displays the number of kilobytes each CPU
buffer can hold. The tracer buffers are the same size
for each CPU. The displayed number is the size of the
- CPU buffer and not total size of all buffers. The
+ 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
@@ -1306,28 +1306,16 @@
number of entries.
# cat /debug/tracing/buffer_size_kb
-65620
+1408 (units kilobytes)
Note, to modify this, you must have tracing completely disabled. To do that,
echo "nop" into the current_tracer. If the current_tracer is not set
to "nop", an EINVAL error will be returned.
# echo nop > /debug/tracing/current_tracer
- # echo 100000 > /debug/tracing/buffer_size_kb
+ # echo 10000 > /debug/tracing/buffer_size_kb
# cat /debug/tracing/buffer_size_kb
-100045
-
-
-Notice that we echoed in 100,000 but the size is 100,045. The entries
-are held in individual pages. It allocates the number of pages it takes
-to fulfill the request. If more entries may fit on the last page
-then they will be added.
-
- # echo 1 > /debug/tracing/buffer_size_kb
- # cat /debug/tracing/buffer_size_kb
-85
-
-This shows us that 85 entries can fit in a single page.
+10000 (units kilobytes)
The number of pages which will be allocated is limited to a percentage
of available memory. Allocating too much will produce an error.