linux-kernel - Re: [patch 0/4] make pr

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Message-ID: <20080211163832.GA10777@redhat.com>
Date:	Mon, 11 Feb 2008 11:38:32 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	Joe Perches <joe@...ches.com>, mathieu.desnoyers@...ymtl.ca,
	akpm@...ux-foundation.org, mingo@...e.hu, fche@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/4] make pr_debug() dynamic

On Sat, Feb 09, 2008 at 11:21:58PM +0100, Jan Engelhardt wrote:
> >> 
> >> What's wrong with klogd -c 8 or equivalent?
> >
> >Setting the loglevel higher, will not make pr_debug() calls visible. The only
> >way to make them visible right now, is by re-compiling the kernel.
> 
> pr_debug() was IMHO meant to be a compile-time optimization
> to throw out debug messages most people do not want.
> 
> If you want to switch on/off debugging messages, use
> printk(KERN_DEBUG) [with klogd -c something] and not pr_debug!

true, we could turn pr_debug() calls into printk(KERN_DEBUG) calls, but there
is an overhead to all these extra printk functions calls. The way I have
implemented pr_debug(), there is no function call at all, in the off case.
To me pr_debug() is currently a compile option, b/c there is often a lot of
overhead to having it on. Being able to turn pr_debug() calls off/on in a
production environment, to get debugging data seems very valuable.

thanks,

-Jason
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