[PATCH 4/7] ring-buffer: Allow ring_buffer_event_time_stamp() to return time stamp of all events

Steven Rostedt
2021-03-12T21:15:42Z

Currently, ring_buffer_event_time_stamp() only returns an accurate time
stamp of the event if it has an absolute extended time stamp attached to
it. To make it more robust, use the event_stamp() in case the event does
not have an absolute value attached to it.

This will allow ring_buffer_event_time_stamp() to be used in more cases
than just histograms, and it will also allow histograms to not require
including absolute values all the time.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
include/linux/ring_buffer.h | 3 +-
kernel/trace/ring_buffer.c | 60 ++++++++++++++++++++++++--------
kernel/trace/trace_events_hist.c | 2 +-
3 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 136ea0997e6d..057b7ed4fe24 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -61,7 +61,8 @@ enum ring_buffer_type {

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);
+u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
+ struct ring_buffer_event *event);

/*
* ring_buffer_discard_commit will remove an event that has not
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 470d97169081..8fa2a84f714f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -298,21 +298,6 @@ static u64 rb_event_time_stamp(struct ring_buffer_event *event)
return ts;
}

-/**
- * 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)
-{
- return rb_event_time_stamp(event);
-}
-
/* Flag when events were overwritten */
#define RB_MISSED_EVENTS (1 << 31)
/* Missed count stored at end */
@@ -757,6 +742,51 @@ static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
}
#endif

+static inline u64 rb_time_stamp(struct trace_buffer *buffer);
+
+/**
+ * ring_buffer_event_time_stamp - return the event's current time stamp
+ * @buffer: The buffer that the event is on
+ * @event: the event to get the time stamp of
+ *
+ * Note, this must be called after @event is reserved, and before it is
+ * committed to the ring buffer. And must be called from the same
+ * context where the event was reserved (normal, softirq, irq, etc).
+ *
+ * Returns the time stamp associated with the current event.
+ * If the event has an extended time stamp, then that is used as
+ * the time stamp to return.
+ * In the highly unlikely case that the event was nested more than
+ * the max nesting, then the write_stamp of the buffer is returned,
+ * otherwise current time is returned, but that really neither of
+ * the last two cases should ever happen.
+ */
+u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
+ struct ring_buffer_event *event)
+{
+ struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[smp_processor_id()];
+ unsigned int nest;
+ u64 ts;
+
+ /* If the event includes an absolute time, then just use that */
+ if (event->type_len == RINGBUF_TYPE_TIME_STAMP)
+ return rb_event_time_stamp(event);
+
+ /* Read the current saved nesting level time stamp */
+ nest = local_read(&cpu_buffer->committing) - 1;
+ if (likely(nest < MAX_NEST))
+ return cpu_buffer->event_stamp[nest];
+
+ WARN_ON_ONCE(1);
+
+ /* Can only fail on 32 bit */
+ if (!rb_time_read(&cpu_buffer->write_stamp, &ts))
+ /* Screw it, just read the current time */
+ ts = rb_time_stamp(cpu_buffer->buffer);
+
+ return ts;
+}
+
/**
* ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
* @buffer: The ring_buffer to get the number of pages from
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index aabad2c93e3a..05ead88cfb66 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -644,7 +644,7 @@ static u64 hist_field_timestamp(struct hist_field *hist_field,
struct hist_trigger_data *hist_data = hist_field->hist_data;
struct trace_array *tr = hist_data->event_file->tr;

- u64 ts = ring_buffer_event_time_stamp(rbe);
+ u64 ts = ring_buffer_event_time_stamp(buffer, rbe);

if (hist_data->attrs->ts_in_usecs && trace_clock_in_ns(tr))
ts = ns2usecs(ts);
--
2.30.1