Message-ID: <49726C56.6080905@zytor.com>
Date: Sat, 17 Jan 2009 15:40:06 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Kyle McMartin <kyle@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Mikael Pettersson <mikpe@it.uu.se>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: "eliminate warn_on_slowpath()" change causes many gcc-3.2.3 warnings
References: <200901171519.n0HFJZuf028704@harpo.it.uu.se> <20090117161817.GA10825@elte.hu> <49723912.6020108@zytor.com> <20090117204421.GA1700@bombadil.infradead.org> <alpine.LFD.2.00.0901181032350.3006@localhost.localdomain>
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Linus Torvalds wrote:
> 
> Don't do this. That just forces a load off a complex pointer instead, with 
> no upsides. At least if it was
> 
> 	extern const char warn_slowpath_nofmt[];
> 
> it would only load the pointer itself, which is still a fairly  expensive 
> op, but at least doesn't require the extra memory load.
> 
> But you'd be better off jusst making it something like
> 
> 	#define NO_FMT ((const char *)(-1))
> 
> instead, which is really much more obvious, and doesn't need any of that 
> "get a pointer" overhead.
> 

At least on x86, the two ops should be the same cost?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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