linux-kernel - [RFC PATCH 0/2 v3] Unified trace buffer

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Date:	Thu, 25 Sep 2008 14:51:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: [RFC PATCH 0/2 v3] Unified trace buffer

[ NOTE function comments have not been updated. Comments within the
 code has.]

This version I change the event header to what Peter Zijlstra requested.
The buffer alignment is now 4 from 8.  The minimum event is 8 bytes.
The event header is now:

struct event_header {
	u32	type:2, len:3, time_delta:27;
	u32	array[];
};

The length of the record is determined as:

  if (data size > 28 bytes)
	lenght = event->array[0] + sizeof(event_header);
  else
  	length = event->len << 4 + sizeof(event_header);

For data

  if (date size > 28 bytes)
	data = &event->array[0];
  else
  	data = &event->array[1];

There are now only 4 internal data types:

0 - Padding
1 - time extent
2 - time stamp
3 - data

This is for internal buffer management only. Other event types should be
pushed to a higher layer, and stored in the data field.

The timing is basically the same as v2 but I added a reader side
ring_buffer_normalize_time_stamp() operation. As a test, I mult the
timestamp to -1, in both set and normalize operations. Whether this
actually tests anything is another story ;-)

I actually like this header and structure the best. And this may be
what I start working on for real.

So please speak up on this one.

I'm going to take a break from this and start doing my real work.
This will let others soak it up for a bit.

-- Steve

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