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 a1b58777839b0e0de19521b934fce0268dbb1591..6d3fe4cdf921a75d51d8f876576d0938ce804a34 100644 (file)
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -94,10 +94,10 @@ of ftrace. Here is a list of some of the key files:
                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 @@ the full size, multiply the number of possible CPUS with the
 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.

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b42d42056fa46477ea6b719a0b5d325e78b1777e..d664aae2e10a067a6097a7e4f2bd68cf1e7d2c31 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2905,7 +2905,7 @@ tracing_entries_read(struct file *filp, char __user *ubuf,
        char buf[64];
        int r;
 
-       r = sprintf(buf, "%lu\n", tr->entries);
+       r = sprintf(buf, "%lu\n", tr->entries >> 10);
        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
@@ -2945,6 +2945,9 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
                        atomic_inc(&max_tr.data[cpu]->disabled);
        }
 
+       /* value is in KB */
+       val <<= 10;
+
        if (val != global_trace.entries) {
                ret = ring_buffer_resize(global_trace.buffer, val);
                if (ret < 0) {