ring_buffer: compressed event header
RB_MAX_SMALL_DATA = 28bytes is too small for most tracers, it wastes
an 'u32' to save the actually length for events which data size > 28.
This fix uses compressed event header and enlarges RB_MAX_SMALL_DATA.
[ Impact: saves about 0%-12.5%(depends on tracer) memory in ring_buffer ]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <49F13189.3090000@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index fac8f1a..1c2f809 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -11,7 +11,7 @@
* Don't refer to this struct directly, use functions below.
*/
struct ring_buffer_event {
- u32 type:2, len:3, time_delta:27;
+ u32 type_len:5, time_delta:27;
u32 array[];
};
@@ -24,7 +24,8 @@
* size is variable depending on how much
* padding is needed
* If time_delta is non zero:
- * everything else same as RINGBUF_TYPE_DATA
+ * array[0] holds the actual length
+ * size = 4 + length (bytes)
*
* @RINGBUF_TYPE_TIME_EXTEND: Extend the time delta
* array[0] = time delta (28 .. 59)
@@ -35,22 +36,23 @@
* array[1..2] = tv_sec
* size = 16 bytes
*
- * @RINGBUF_TYPE_DATA: Data record
- * If len is zero:
+ * <= @RINGBUF_TYPE_DATA_TYPE_LEN_MAX:
+ * Data record
+ * If type_len is zero:
* array[0] holds the actual length
* array[1..(length+3)/4] holds data
- * size = 4 + 4 + length (bytes)
+ * size = 4 + length (bytes)
* else
- * length = len << 2
+ * length = type_len << 2
* array[0..(length+3)/4-1] holds data
* size = 4 + length (bytes)
*/
enum ring_buffer_type {
+ RINGBUF_TYPE_DATA_TYPE_LEN_MAX = 28,
RINGBUF_TYPE_PADDING,
RINGBUF_TYPE_TIME_EXTEND,
/* FIXME: RINGBUF_TYPE_TIME_STAMP not implemented */
RINGBUF_TYPE_TIME_STAMP,
- RINGBUF_TYPE_DATA,
};
unsigned ring_buffer_event_length(struct ring_buffer_event *event);