linux-kernel - Re: [PATCH] Fix WARN_ON / WARN_ON

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Message-ID: <45231299.1000601@yahoo.com.au>
Date:	Wed, 04 Oct 2006 11:47:05 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...l.org>
CC:	tim.c.chen@...ux.intel.com, herbert@...dor.apana.org.au,
	linux-kernel@...r.kernel.org, leonid.i.ananiev@...el.com
Subject: Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

Andrew Morton wrote:
> On Tue, 03 Oct 2006 17:09:29 -0700
> Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> 
> 
>>On Tue, 2006-10-03 at 17:07 -0700, Andrew Morton wrote:
>>
>>
>>>Perhaps the `static int __warn_once' is getting put in the same cacheline
>>>as some frequently-modified thing.   Perhaps try marking that as __read_mostly?
>>>
>>
>>I've tried marking static int __warn_once as __read_mostly.  However, it
>>did not help with reducing the cache miss :(
>>
>>So I would suggest reversing the "Let WARN_ON/WARN_ON_ONCE return the
>>condition" patch.  It has just been added 3 days ago so reversing it
>>should not be a problem.
>>
> 
> 
> Not yet, please.  This is presently a mystery, and we need to work out
> what's going on.

Still, it seems kind of odd to add this IMO. Especially the WARN_ON_ONCE
makes the if statement less readable.

   if (WARN_ON_ONCE(blah)) {
   }

What does that mean? Without looking at the implementation, that says
the condition is true at most once, when the warning is printed.

What's wrong with adding WARN and WARN_ONCE, and eating the single extra
line? You're always telling people to do that with assignments (which I
agree with, but are _more_ readable than this WARN_ON_ONCE thing).

-- 
SUSE Labs, Novell Inc.
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