linux-kernel - Re: [PATCH 3/3] ring-buffer: add design document

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Date:	Wed, 10 Jun 2009 23:25:46 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Christoph Hellwig <hch@...radead.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Huang Ying <ying.huang@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH 3/3] ring-buffer: add design document


On Thu, 11 Jun 2009, Hidetoshi Seto wrote:
> Steven Rostedt wrote:
> > +
> > +  +------+
> > +  |reader|          RING BUFFER
> > +  |page  |-------------------+
> > +  +------+ <---------------+ v
> > +    |  ^          +---+   +---+   +---+
> > +    |  |          |   |-->|   |-->|   |
> > +    |  |          |   |<--|   |<--|   |<-+
> > +    |  |          +---+   +---+   +---+  |
> > +    |  |             |             ^ |   |
> > +    |  |             +-------------+ |   |
> > +    |  +-----------------------------+   |
> > +    +------------------------------------+
> 
> It seems the middle of three pages have 2 prev arrows... ?

Yes that is a mistake. Thanks, I'll fix it.
> > +
> > +It does a cmpxchg with the pointer to the previous head page to make it
> > +point to the reader page. Note that the new pointer does not have the HEADER
> > +flag set.  This action atomically moves the head page forward.
> > +
> > +  +------+
> > +  |reader|          RING BUFFER
> > +  |page  |-------H-----------+
> > +  +------+ <---------------+ v
> > +    |  ^          +---+   +---+   +---+
> > +    |  |          |   |-->|   |-->|   |
> > +    |  |          |   |<--|   |<--|   |<-+
> > +    |  |          +---+   +---+   +---+  |
> > +    |  |             |             ^ |   |
> > +    |  |             +-------------+ |   |
> > +    |  +-----------------------------+   |
> > +    +------------------------------------+
> > +
> 
> Ditto.

Ditto too ;-)

Thanks,

-- Steve

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