ring-buffer: Redefine the unimplemented RINGBUF_TYPE_TIME_STAMP

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>

1 files changed, 76 insertions, 28 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2a03e069bbc6..33073cdebb26 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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);
 
@@ -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;
@@ -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);
@@ -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);
@@ -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 */
@@ -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 */
@@ -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 {
@@ -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;
         }
@@ -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 */
@@ -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;
         }
@@ -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 */
@@ -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);
@@ -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:
@@ -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:
@@ -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.
@@ -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);
@@ -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;
 
@@ -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);