linux-kernel - Re: [git pull] sparseirq / irq updates for v2.6.29

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Message-ID: <20081229093425.GB27293@elte.hu>
Date:	Mon, 29 Dec 2008 10:34:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Subject: Re: [git pull] sparseirq / irq updates for v2.6.29


* Yinghai Lu <yinghai@...nel.org> wrote:

> On Sun, Dec 28, 2008 at 3:55 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > Ingo Molnar wrote:
> >>
> >> ok, agreed. I was hoping for some more generic workaround but nothing
> >> seemed to keep gcc from inlining such functions.
> >>
> >
> > Other than blacklisting those gcc versions.  It's pretty easy to
> > understand how a bug like that could creep in, since one of the main
> > improvements of the early gcc4 series was better inlining as an
> > optimization.
> 
> 1. one time path add one dummy printk

dummy printks are not a good idea at all. Often the weak versions are the 
ones that get used and it would be very annoying if there was a per boot 
(or even per syscall!) 'dummy printk'.

> 2. multi path, could move it to another file.
> could add one like kernel/weak.c to collect those ...

that pretty much removes the advantages of __weak symbols: to provide 
default implementations for various functionality, without having to do
#ifdefs. The default implementation will often want to be near the usage
site - so these bugs will reoccur again and again.

	Ingo
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