linux-kernel - Re: [RFC] Unified Ring Buffer (Next Generation)

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Date:	Wed, 19 May 2010 15:38:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [RFC] Unified Ring Buffer (Next Generation)

On Wed, 2010-05-19 at 21:25 +0200, Andi Kleen wrote:

> > Perhaps, but the goal is actually to handle all the features of perf and
> > ftrace in a generic fashion.
> 
> Ok so your goal is to only cover perf and ftrace and let all 
> the other users be alone? 
> 

Yes, my goal is to unify perf and ftrace, but that's because that is
what I am working most on.

> > 
> > You also bring up a point that I try very hard to get across. When
> > people think of a ring buffer, they think of the ones that they created
> > in CS101, not realizing that when you are dealing with production
> > systems, handling the requirements makes the buffering much more
> > complex.
> 
> For most users the simple ones are totally adequate though.
> 
> > Perhaps the answer is we are fine with more than one ring buffer. I'm OK
> 
> That's what we already have in fact: kfifo, ftrace, perf, a couple
> of private ones all over.
> 
> I think a couple of private ones could be converted to kfifo
> (I did some of that for my own code) 
> 
> But I don't really see how you can marry the simple kfifo world
> to the highend bells'n'whistles ftrace world. And even in the highend
> world there might be space for multiple specialized ones.
> 
> On the other hand if the highend world had less overhead
> then at least some of the "higher end" kfifo users could start 
> considering to use it.

If Mathieu can pull off the requirements that can handle all of ftrace
and perf in a light weight manner, then great. But if the end result is
still to much for these "private" users, then we should have a
"ring_buffer_lite", and perhaps even base it off of a kfifo itself.

Note, it would be nice to have a single location that (a) ring buffer(s)
reside at. This way if a developer has a need for a ring buffer then
they can have a single location to look for one.

Maybe the ring buffer code should go in lib/ringbuffers/ instead of
kernel/ringbuffer/.

-- Steve


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