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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>
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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);

83
kernel/trace/ring_buffer.c
View File

@ -28,8 +28,8 @@ int ring_buffer_print_entry_header(struct trace_seq *s)
{
int ret;
ret = trace_seq_printf(s, "\ttype : 2 bits\n");
ret = trace_seq_printf(s, "\tlen : 3 bits\n");
ret = trace_seq_printf(s, "# compressed entry header\n");
ret = trace_seq_printf(s, "\ttype_len : 5 bits\n");
ret = trace_seq_printf(s, "\ttime_delta : 27 bits\n");
ret = trace_seq_printf(s, "\tarray : 32 bits\n");
ret = trace_seq_printf(s, "\n");
@ -37,8 +37,8 @@ int ring_buffer_print_entry_header(struct trace_seq *s)
RINGBUF_TYPE_PADDING);
ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
RINGBUF_TYPE_TIME_EXTEND);
ret = trace_seq_printf(s, "\tdata : type == %d\n",
RINGBUF_TYPE_DATA);
ret = trace_seq_printf(s, "\tdata max type_len == %d\n",
RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
return ret;
}
@ -204,7 +204,10 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
#define RB_ALIGNMENT 4U
#define RB_MAX_SMALL_DATA 28
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
enum {
RB_LEN_TIME_EXTEND = 8,
@ -213,17 +216,18 @@ enum {
static inline int rb_null_event(struct ring_buffer_event *event)
{
return event->type == RINGBUF_TYPE_PADDING && event->time_delta == 0;
return event->type_len == RINGBUF_TYPE_PADDING
&& event->time_delta == 0;
}
static inline int rb_discarded_event(struct ring_buffer_event *event)
{
return event->type == RINGBUF_TYPE_PADDING && event->time_delta;
return event->type_len == RINGBUF_TYPE_PADDING && event->time_delta;
}
static void rb_event_set_padding(struct ring_buffer_event *event)
{
event->type = RINGBUF_TYPE_PADDING;
event->type_len = RINGBUF_TYPE_PADDING;
event->time_delta = 0;
}
@ -232,8 +236,8 @@ rb_event_data_length(struct ring_buffer_event *event)
{
unsigned length;
if (event->len)
length = event->len * RB_ALIGNMENT;
if (event->type_len)
length = event->type_len * RB_ALIGNMENT;
else
length = event->array[0];
return length + RB_EVNT_HDR_SIZE;
@ -243,12 +247,12 @@ rb_event_data_length(struct ring_buffer_event *event)
static unsigned
rb_event_length(struct ring_buffer_event *event)
{
switch (event->type) {
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
/* undefined */
return -1;
return rb_event_data_length(event);
return event->array[0] + RB_EVNT_HDR_SIZE;
case RINGBUF_TYPE_TIME_EXTEND:
return RB_LEN_TIME_EXTEND;
@ -272,7 +276,7 @@ rb_event_length(struct ring_buffer_event *event)
unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
unsigned length = rb_event_length(event);
if (event->type != RINGBUF_TYPE_DATA)
if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
return length;
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
@ -285,9 +289,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_length);
static void *
rb_event_data(struct ring_buffer_event *event)
{
BUG_ON(event->type != RINGBUF_TYPE_DATA);
BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
/* If length is in len field, then array[0] has the data */
if (event->len)
if (event->type_len)
return (void *)&event->array[0];
/* Otherwise length is in array[0] and array[1] has the data */
return (void *)&event->array[1];
@ -988,7 +992,7 @@ static void rb_update_overflow(struct ring_buffer_per_cpu *cpu_buffer)
if (RB_WARN_ON(cpu_buffer, rb_null_event(event)))
return;
/* Only count data entries */
if (event->type != RINGBUF_TYPE_DATA)
if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
continue;
cpu_buffer->overrun++;
cpu_buffer->entries--;
@ -1133,28 +1137,21 @@ static void
rb_update_event(struct ring_buffer_event *event,
unsigned type, unsigned length)
{
event->type = type;
event->type_len = type;
switch (type) {
case RINGBUF_TYPE_PADDING:
break;
case RINGBUF_TYPE_TIME_EXTEND:
event->len = DIV_ROUND_UP(RB_LEN_TIME_EXTEND, RB_ALIGNMENT);
break;
case RINGBUF_TYPE_TIME_STAMP:
event->len = DIV_ROUND_UP(RB_LEN_TIME_STAMP, RB_ALIGNMENT);
break;
case RINGBUF_TYPE_DATA:
case 0:
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA) {
event->len = 0;
if (length > RB_MAX_SMALL_DATA)
event->array[0] = length;
} else
event->len = DIV_ROUND_UP(length, RB_ALIGNMENT);
else
event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
break;
default:
BUG();
@ -1562,7 +1559,7 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
if (length > BUF_PAGE_SIZE)
goto out;
event = rb_reserve_next_event(cpu_buffer, RINGBUF_TYPE_DATA, length);
event = rb_reserve_next_event(cpu_buffer, 0, length);
if (!event)
goto out;
@ -1634,7 +1631,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
static inline void rb_event_discard(struct ring_buffer_event *event)
{
event->type = RINGBUF_TYPE_PADDING;
/* array[0] holds the actual length for the discarded event */
event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
event->type_len = RINGBUF_TYPE_PADDING;
/* time delta must be non zero */
if (!event->time_delta)
event->time_delta = 1;
@ -1786,8 +1785,7 @@ int ring_buffer_write(struct ring_buffer *buffer,
goto out;
event_length = rb_calculate_event_length(length);
event = rb_reserve_next_event(cpu_buffer,
RINGBUF_TYPE_DATA, event_length);
event = rb_reserve_next_event(cpu_buffer, 0, event_length);
if (!event)
goto out;
@ -2035,7 +2033,7 @@ rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
{
u64 delta;
switch (event->type) {
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
@ -2066,7 +2064,7 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
{
u64 delta;
switch (event->type) {
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
@ -2181,7 +2179,8 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
event = rb_reader_event(cpu_buffer);
if (event->type == RINGBUF_TYPE_DATA || rb_discarded_event(event))
if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX
|| rb_discarded_event(event))
cpu_buffer->entries--;
rb_update_read_stamp(cpu_buffer, event);
@ -2262,7 +2261,7 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
event = rb_reader_event(cpu_buffer);
switch (event->type) {
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
RB_WARN_ON(cpu_buffer, 1);
@ -2334,7 +2333,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
event = rb_iter_head_event(iter);
switch (event->type) {
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event)) {
rb_inc_iter(iter);
@ -2393,7 +2392,7 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
event = rb_buffer_peek(buffer, cpu, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (event && event->type == RINGBUF_TYPE_PADDING) {
if (event && event->type_len == RINGBUF_TYPE_PADDING) {
cpu_relax();
goto again;
}
@ -2421,7 +2420,7 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
event = rb_iter_peek(iter, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (event && event->type == RINGBUF_TYPE_PADDING) {
if (event && event->type_len == RINGBUF_TYPE_PADDING) {
cpu_relax();
goto again;
}
@ -2466,7 +2465,7 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
out:
preempt_enable();
if (event && event->type == RINGBUF_TYPE_PADDING) {
if (event && event->type_len == RINGBUF_TYPE_PADDING) {
cpu_relax();
goto again;
}
@ -2559,7 +2558,7 @@ ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (event && event->type == RINGBUF_TYPE_PADDING) {
if (event && event->type_len == RINGBUF_TYPE_PADDING) {
cpu_relax();
goto again;
}
@ -2766,7 +2765,7 @@ static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
if (RB_WARN_ON(cpu_buffer, rb_null_event(event)))
return;
/* Only count data entries */
if (event->type != RINGBUF_TYPE_DATA)
if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
continue;
cpu_buffer->entries--;
}