linux-kernel - Re: [RFC PATCH 1/3] Unified trace buffer

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Date:	Sat, 27 Sep 2008 14:18:25 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Martin Bligh <mbligh@...gle.com>,
	Martin Bligh <mbligh@...igh.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Tom Zanussi <zanussi@...cast.net>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH 1/3] Unified trace buffer

On Sat, 27 Sep 2008, Peter Zijlstra wrote:

> On Sat, 2008-09-27 at 13:38 -0400, Steven Rostedt wrote:
> 
> >  It does not even implement the merge sort. That's up to the 
> > tracer to handle. 
> 
> You could though, as you have the timestamps..

Yep, and the first version did just that. I could add it back, but it gets 
interesting if we want to read from a buffer not on the same CPU, if we 
want to implement lockless.

I started (but pushed it aside) a tracing_buffer.c layer, that would do 
the merges and such based on the timestamps, as well as events and event
registration. It was because of you that I pulled this stuff out of the 
bottom ring buffer layer ;-)

 > 
> > So yes, the tracer can implement anything it wants on top of the ring 
> > buffer ;-)
> 
> Mathieu seems to disagree, it would be good if he can share some
> specifics so we can work on resolving those.

Mathieu always disagrees ;-)

Well the ring buffer interface should never interact directly with the 
user interface. There should always be a layer between the buffer and the 
user interface. This means that V2 can change drastically from V1. But I 
want V1 to get in now so that we can start unifying the existing tracers 
in the kernel.

Also, I like Linus's proposal that anything bigger than a page needs to be 
kept outside the ring buffer and the ring buffer can simply add a pointer 
to it.

-- Steve

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