linux-kernel - Re: [PATCH v6] Unified trace buffer

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Date:	Fri, 26 Sep 2008 12:30:34 -0600
From:	Richard Holden <aciddeath@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <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>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v6] Unified trace buffer

On 9/26/08 12:05 PM, "Steven Rostedt" <rostedt@...dmis.org> wrote:

> ring_buffer_alloc: create a new ring buffer. Can choose between
> overwrite or consumer/producer mode. Overwrite will
> overwrite old data, where as consumer producer will
> throw away new data if the consumer catches up with the
> producer.  The consumer/producer is the default.

Forgive me if I've gotten this wrong but the terminology seems backwards
Here, I would think we only throw away new data if the producer catches up
with the consumer, if the consumer catches up with the producer we're
reading data as fast as it's being written.

> 
> ring_buffer_write: writes some data into the ring buffer.
> 
> ring_buffer_peek: Look at a next item in the cpu buffer.
> ring_buffer_consume: get the next item in the cpu buffer and
> consume it. That is, this function increments the head
> pointer.

Here too, I would think that consuming data would modify the tail pointer.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>

Just trying to understand the terminology before I look at the code so I'm
sorry if I have just completely misunderstood.

-Richard Holden


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