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ring_buffer: compressed event header

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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>
This commit is contained in:
Lai Jiangshan 2009-04-24 11:27:05 +08:00 • committed by Steven Rostedt
parent c2518c4366
commit 334d4169a6
2 changed files with 50 additions and 49 deletions
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16
include/linux/ring_buffer.h
View file

@ -11,7 +11,7 @@ struct ring_buffer_iter;
* 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 @@ struct ring_buffer_event {
* 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 @@ struct ring_buffer_event {
* 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);