linux-kernel - Re: [PATCH] "volatile considered harmful", take 2

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Message-ID: <46447509.7010305@gmail.com>
Date:	Fri, 11 May 2007 19:22:09 +0530
From:	jimmy bahuleyan <knight.camelot@...il.com>
To:	Johannes Stezenbach <js@...uxtv.org>
CC:	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Jesper Juhl <jesper.juhl@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Heikki Orsila <shdl@...alwe.fi>,
	"H. Peter Anvin" <hpa@...or.com>,
	Satyam Sharma <satyam.sharma@...il.com>
Subject: Re: [PATCH] "volatile considered harmful", take 2

Johannes Stezenbach wrote:
> On Fri, May 11, 2007 at 02:08:54AM +0530, jimmy bahuleyan wrote:
>> Jonathan Corbet wrote:
>> [snip..]
>>> +
>>> +  - The jiffies variable is special in that it can have a different value
>>> +    every time it is referenced, but it can be read without any special
>>> +    locking.  So jiffies can be volatile, but the addition of other
>>> +    variables of this type is strongly frowned upon.  Jiffies is considered
>>> +    to be a "stupid legacy" issue in this regard.
>> Why is it that you consider jiffies to be a "stupid legacy"? Isn't it
>> natural to have a externally modified variable which is only /read/ to
>> be volatile? (or is jiffies supposed to be replaced with something
>> smarter/better :)
> 
> "stupid legacy" were Linus' words. http://lwn.net/Articles/233482/
> 
> How about this:
> 
> "The jiffies variable is a special case because there are too
> many places in the kernel which would have to be changed and reviewed
> if the volatile would be removed from jiffies. However, the
> use of volatile qualifier for jiffies is just as wrong as
> it is elsewhere. Don't use jiffies as an excuse to use volatile
> in your code."
> 
> 
> Johannes
> 

yes this sounds better. at least to a non-kernel expert like me it makes
the meaning clear - 'that jiffies is a special case, not to be taken as
an example for other stuff'.

-jb

-- 
Tact is the art of making a point without making an enemy.
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