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ring-buffer: Redefine the unimplemented RINGBUF_TYPE_TIME_STAMP
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RINGBUF_TYPE_TIME_STAMP is defined but not used, and from what I can
gather was reserved for something like an absolute timestamp feature
for the ring buffer, if not a complete replacement of the current
time_delta scheme.

This code redefines RINGBUF_TYPE_TIME_STAMP to implement absolute time
stamps.  Another way to look at it is that it essentially forces
extended time_deltas for all events.

The motivation for doing this is to enable time_deltas that aren't
dependent on previous events in the ring buffer, making it feasible to
use the ring_buffer_event timetamps in a more random-access way, for
purposes other than serial event printing.

To set/reset this mode, use tracing_set_timestamp_abs() from the
previous interface patch.

Link: http://lkml.kernel.org/r/477b362dba1ce7fab9889a1a8e885a62c472f041.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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@tzanussi @rostedt
tzanussi authored and rostedt committed Mar 10, 2018
1 parent 00b4145 commit dc4e280
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Showing 2 changed files with 83 additions and 33 deletions.
12 changes: 7 additions & 5 deletions include/linux/ring_buffer.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,10 +34,12 @@ struct ring_buffer_event {
* array[0] = time delta (28 .. 59)
* size = 8 bytes
*
* @RINGBUF_TYPE_TIME_STAMP: Sync time stamp with external clock
* array[0] = tv_nsec
* array[1..2] = tv_sec
* size = 16 bytes
* @RINGBUF_TYPE_TIME_STAMP: Absolute timestamp
* Same format as TIME_EXTEND except that the
* value is an absolute timestamp, not a delta
* event.time_delta contains bottom 27 bits
* array[0] = top (28 .. 59) bits
* size = 8 bytes
*
* <= @RINGBUF_TYPE_DATA_TYPE_LEN_MAX:
* Data record
Expand All @@ -54,12 +56,12 @@ 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,
};

unsigned ring_buffer_event_length(struct ring_buffer_event *event);
void *ring_buffer_event_data(struct ring_buffer_event *event);
u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event);

/*
* ring_buffer_discard_commit will remove an event that has not
Expand Down
104 changes: 76 additions & 28 deletions kernel/trace/ring_buffer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,8 @@ int ring_buffer_print_entry_header(struct trace_seq *s)
RINGBUF_TYPE_PADDING);
trace_seq_printf(s, "\ttime_extend : type == %d\n",
RINGBUF_TYPE_TIME_EXTEND);
trace_seq_printf(s, "\ttime_stamp : type == %d\n",
RINGBUF_TYPE_TIME_STAMP);
trace_seq_printf(s, "\tdata max type_len == %d\n",
RINGBUF_TYPE_DATA_TYPE_LEN_MAX);

Expand Down Expand Up @@ -140,12 +142,15 @@ int ring_buffer_print_entry_header(struct trace_seq *s)

enum {
RB_LEN_TIME_EXTEND = 8,
RB_LEN_TIME_STAMP = 16,
RB_LEN_TIME_STAMP = 8,
};

#define skip_time_extend(event) \
((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))

#define extended_time(event) \
(event->type_len >= RINGBUF_TYPE_TIME_EXTEND)

static inline int rb_null_event(struct ring_buffer_event *event)
{
return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
Expand Down Expand Up @@ -209,7 +214,7 @@ rb_event_ts_length(struct ring_buffer_event *event)
{
unsigned len = 0;

if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
if (extended_time(event)) {
/* time extends include the data event after it */
len = RB_LEN_TIME_EXTEND;
event = skip_time_extend(event);
Expand All @@ -231,7 +236,7 @@ unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
unsigned length;

if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
if (extended_time(event))
event = skip_time_extend(event);

length = rb_event_length(event);
Expand All @@ -248,7 +253,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_length);
static __always_inline void *
rb_event_data(struct ring_buffer_event *event)
{
if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
if (extended_time(event))
event = skip_time_extend(event);
BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
/* If length is in len field, then array[0] has the data */
Expand All @@ -275,6 +280,27 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)

/**
* ring_buffer_event_time_stamp - return the event's extended timestamp
* @event: the event to get the timestamp of
*
* Returns the extended timestamp associated with a data event.
* An extended time_stamp is a 64-bit timestamp represented
* internally in a special way that makes the best use of space
* contained within a ring buffer event. This function decodes
* it and maps it to a straight u64 value.
*/
u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event)
{
u64 ts;

ts = event->array[0];
ts <<= TS_SHIFT;
ts += event->time_delta;

return ts;
}

/* Flag when events were overwritten */
#define RB_MISSED_EVENTS (1 << 31)
/* Missed count stored at end */
Expand Down Expand Up @@ -2217,12 +2243,15 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,

/* Slow path, do not inline */
static noinline struct ring_buffer_event *
rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
{
event->type_len = RINGBUF_TYPE_TIME_EXTEND;
if (abs)
event->type_len = RINGBUF_TYPE_TIME_STAMP;
else
event->type_len = RINGBUF_TYPE_TIME_EXTEND;

/* Not the first event on the page? */
if (rb_event_index(event)) {
/* Not the first event on the page, or not delta? */
if (abs || rb_event_index(event)) {
event->time_delta = delta & TS_MASK;
event->array[0] = delta >> TS_SHIFT;
} else {
Expand Down Expand Up @@ -2265,7 +2294,9 @@ rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
* add it to the start of the resevered space.
*/
if (unlikely(info->add_timestamp)) {
event = rb_add_time_stamp(event, delta);
bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer);

event = rb_add_time_stamp(event, info->delta, abs);
length -= RB_LEN_TIME_EXTEND;
delta = 0;
}
Expand Down Expand Up @@ -2453,7 +2484,7 @@ static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer

static inline void rb_event_discard(struct ring_buffer_event *event)
{
if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
if (extended_time(event))
event = skip_time_extend(event);

/* array[0] holds the actual length for the discarded event */
Expand Down Expand Up @@ -2497,10 +2528,11 @@ rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
cpu_buffer->write_stamp =
cpu_buffer->commit_page->page->time_stamp;
else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
delta = ring_buffer_event_time_stamp(event);
cpu_buffer->write_stamp += delta;
} else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
delta = ring_buffer_event_time_stamp(event);
cpu_buffer->write_stamp = delta;
} else
cpu_buffer->write_stamp += event->time_delta;
}
Expand Down Expand Up @@ -2680,7 +2712,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
* If this is the first commit on the page, then it has the same
* timestamp as the page itself.
*/
if (!tail)
if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer))
info->delta = 0;

/* See if we shot pass the end of this buffer page */
Expand Down Expand Up @@ -2757,8 +2789,11 @@ rb_reserve_next_event(struct ring_buffer *buffer,
/* make sure this diff is calculated here */
barrier();

/* Did the write stamp get updated already? */
if (likely(info.ts >= cpu_buffer->write_stamp)) {
if (ring_buffer_time_stamp_abs(buffer)) {
info.delta = info.ts;
rb_handle_timestamp(cpu_buffer, &info);
} else /* Did the write stamp get updated already? */
if (likely(info.ts >= cpu_buffer->write_stamp)) {
info.delta = diff;
if (unlikely(test_time_stamp(info.delta)))
rb_handle_timestamp(cpu_buffer, &info);
Expand Down Expand Up @@ -3440,14 +3475,13 @@ rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
return;

case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
delta = ring_buffer_event_time_stamp(event);
cpu_buffer->read_stamp += delta;
return;

case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
delta = ring_buffer_event_time_stamp(event);
cpu_buffer->read_stamp = delta;
return;

case RINGBUF_TYPE_DATA:
Expand All @@ -3471,14 +3505,13 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
return;

case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
delta = ring_buffer_event_time_stamp(event);
iter->read_stamp += delta;
return;

case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
delta = ring_buffer_event_time_stamp(event);
iter->read_stamp = delta;
return;

case RINGBUF_TYPE_DATA:
Expand Down Expand Up @@ -3702,6 +3735,8 @@ rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
struct buffer_page *reader;
int nr_loops = 0;

if (ts)
*ts = 0;
again:
/*
* We repeat when a time extend is encountered.
Expand Down Expand Up @@ -3738,12 +3773,17 @@ rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
goto again;

case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
if (ts) {
*ts = ring_buffer_event_time_stamp(event);
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
/* Internal data, OK to advance */
rb_advance_reader(cpu_buffer);
goto again;

case RINGBUF_TYPE_DATA:
if (ts) {
if (ts && !(*ts)) {
*ts = cpu_buffer->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
Expand All @@ -3768,6 +3808,9 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
struct ring_buffer_event *event;
int nr_loops = 0;

if (ts)
*ts = 0;

cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;

Expand Down Expand Up @@ -3820,12 +3863,17 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
goto again;

case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
if (ts) {
*ts = ring_buffer_event_time_stamp(event);
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
/* Internal data, OK to advance */
rb_advance_iter(iter);
goto again;

case RINGBUF_TYPE_DATA:
if (ts) {
if (ts && !(*ts)) {
*ts = iter->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(buffer,
cpu_buffer->cpu, ts);
Expand Down

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