linux-kernel - Re: [PATCH 1/3] ring-buffer: add counters for commit overrun and nmi dropped entries

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Date:	Thu, 30 Apr 2009 23:55:35 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH 1/3] ring-buffer: add counters for commit overrun and
 nmi dropped entries


On Thu, 30 Apr 2009, Andrew Morton wrote:

> On Thu, 30 Apr 2009 23:33:31 -0400 (EDT) Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > > Should you decide to retire the paste pot, and if you can bear to move
> > > `struct ring_buffer' into a header, these four functions could be made
> > > static inlines, with pleasant runtime results.
> > 
> > Well, the only users of these functions are those that output to user 
> > land. The latency format and the stat file.
> 
> OK, that's slowpath.  They were exported to modules - are these files a
> per-tracer thing?

A ring buffer can be allocated per tracer (although ftrace does not -yet- 
do this). Some of these are for per_cpu parts of the ring buffer. The ring 
buffer has a buffer per cpu.

As for the EXPORT_SYMBOLs. See this commit (and I added Robert to the Cc)

commit c4f50183f90fb1fd99aa5941f01b90cd1b882d2e
Author: Robert Richter <robert.richter@....com>
Date:   Thu Dec 11 16:49:22 2008 +0100

    ring_buffer: adding EXPORT_SYMBOLs
    
    I added EXPORT_SYMBOL_GPLs for all functions part of the API
    (ring_buffer.h). This is required since oprofile is using the ring
    buffer and the compilation as modules would fail otherwise.
    
    Signed-off-by: Robert Richter <robert.richter@....com>
    Signed-off-by: Ingo Molnar <mingo@...e.hu>


So it looks like it was just a "give modules all access to the ring 
buffer" commit.

-- Steve

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