Messages in this thread | | | Date | Thu, 7 Sep 2017 10:35:10 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2 08/40] ring-buffer: Redefine the unimplemented RINGBUF_TIME_TIME_STAMP |
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On Tue, 5 Sep 2017 16:57:20 -0500 Tom Zanussi <tom.zanussi@linux.intel.com> wrote: > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > index 28e3472..74bc276 100644 > --- a/include/linux/ring_buffer.h > +++ b/include/linux/ring_buffer.h > @@ -36,10 +36,12 @@ 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
Is it going to be an issue that our time stamp is only 59 bits?
2^59 = 576,460,752,303,423,488
Thus, 2^59 nanoseconds (I doubt we will need to have precision better than nanoseconds) = 576,460,752 seconds = 9,607,679 minutes = 160,127 hours = 6,671 days = 18 years.
We would be screwed if we trace for more than 18 years. ;-)
That's why I had it as 16 bytes, to be able to hold a full 64 bit timestamp (and still be 8 byte aligned). But since we've gone this long without needing this, I'm sure a 59 bit absolute timestamp should be good enough.
> * > * <= @RINGBUF_TYPE_DATA_TYPE_LEN_MAX: > * Data record > @@ -56,12 +58,12 @@ 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
> @@ -2488,6 +2519,10 @@ static inline void rb_event_discard(struct ring_buffer_event *event) > { > u64 delta; > > + /* In TIME_STAMP mode, write_stamp is unused, nothing to do */
No, we still need to keep the write_stamp updated. Sure, it doesn't use it, but I do want to have absolute and delta timestamps working together in a single buffer. It shouldn't be one or the other. In fact, I plan on using it that way for nested events.
Maybe for this feature we can let it slide. But I will be working on fixing that.
-- Steve
> + if (event->type_len == RINGBUF_TYPE_TIME_STAMP) > + return; > + > /* > * The event first in the commit queue updates the > * time stamp. > @@ -2501,9 +2536,7 @@ static inline void rb_event_discard(struct ring_buffer_event *event) > 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
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