linux-kernel - Re: [PATCH 2/9] ext4: Use pr_fmt and pr

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Date:	Thu, 22 Mar 2012 18:02:22 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Joe Perches <joe@...ches.com>
CC:	Jiri Slaby <jirislaby@...il.com>, Ted Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] ext4: Use pr_fmt and pr_<level>

On 03/20/2012 10:46 AM, Joe Perches wrote:
> On Tue, 2012-03-20 at 10:25 +0100, Jiri Slaby wrote:
>> On 03/20/2012 10:21 AM, Joe Perches wrote:
>>> the ath5k pr_ conversion patches are to
>>> standardize prefixes and to reduce code size by
>>> centralizing tests.
>>
>> What is the "standard" prefix?
> 
> KBUILD_MODNAME

Instead, we should switch as many printks to dev_* and similar as
possible, right? They are standard and provide a good interface for
extensions: one has a device to work with. This is something what pr_*
does not offer. For that reason it's not worth it.

>>> https://lkml.org/lkml/2012/3/18/121
>>> https://lkml.org/lkml/2012/3/18/123
>>> https://lkml.org/lkml/2012/3/18/124
>>> I happen to like 30K/10+% code size reductions.
>> Obvious question: what speed reduction does this bring?
> 
> Anyone looking for speed impacts in logging
> messages is looking in the wrong place.

Ok, I finally found some time to look into the changes properly. I was
confused by Adrian's note that you moved a debug check to an external
function. But that is not true.

> btw: it's effectively 0.

Frankly, moving the debug code to a separate function should make the
code rather faster. By moving the unlikely code out of the instruction
cache.

thanks,
-- js suse labs

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