linux-kernel - Re: [Cbe-oss-dev] [PATCH, RFC] sputrace: use the generic event tracer

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Message-ID: <20090510190705.GA23659@lst.de>
Date:	Sun, 10 May 2009 21:07:05 +0200
From:	Christoph Hellwig <hch@....de>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	Christoph Hellwig <hch@....de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	cbe-oss-dev@...abs.org
Subject: Re: [Cbe-oss-dev] [PATCH, RFC] sputrace: use the generic event tracer

On Wed, May 06, 2009 at 03:05:39PM -0400, Steven Rostedt wrote:
> The worry is if this is used by modules. A constant string may not be
> around when the buffer is read.
> 
> This should not be a problem because the formatting of the string is not
> around either, and we just output 'unknown type'.  But I may be adding
> code when a module is unloaded to reset the ring buffer if the module
> registered any events. That's because we have other races to worry
> about.

I think having some constant string description for trace events is
pretty common and used in just above any ad-hoc tracer I've seen,
and just storing the pointers makes this a lot more efficient.

So either we try to make sure this works, or we need some big waivers
in the documentation that people need to use the slower __string
variant.

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