linux-kernel - Re: [PATCH] plist: replace pr_debug with printk in plist

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Date:	Wed, 07 May 2014 11:10:38 -0700
From:	Joe Perches <joe@...ches.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Dan Streetman <ddstreet@...e.org>,
	Fabian Frederick <fabf@...net.be>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <borislav.petkov@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] plist: replace pr_debug with printk in plist_test()

On Wed, 2014-05-07 at 10:35 -0400, Steven Rostedt wrote:
> On Wed, 7 May 2014 10:21:28 -0400 Dan Streetman <ddstreet@...e.org> wrote:

> > It would be even better if the note could clarify that sometimes it is
> > ok to use printk(KERN_DEBUG
> 
> Exactly. I think it's rather stupid to have to do a #define DEBUG to
> have pr_debug() print in general.
> 
> I see no reason to have pr_debug() be anything different than the other
> pr_*() functions.

pr_debug is meant to be disabled and have _no_ runtime
effect unless DEBUG is #defined.

For embedded systems where printk is enabled, pr_debug
does have some utility for code/text reduction and it
can have a minor impact on performance.

tracing is frequently a better option for development
and is often a better runtime tool.

CONFIG_DYNAMIC_DEBUG is not enabled by default in most
defconfigs.

The _only_ reason it's possible is because dynamic debug
is runtime patched to be fairly cost free for relatively
larger memory/higher performance systems.

> The plist code is a perfect scenario where printk(KERN_DEBUG...) is
> appropriate, and using pr_debug() with a hard coded #define DEBUG is
> just stupid.

yup.


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