linux-kernel - Re: "eliminate warn_on_slowpath()" change causes many gcc-3.2.3 warnings

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Date:	Sat, 17 Jan 2009 15:40:06 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Kyle McMartin <kyle@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Mikael Pettersson <mikpe@...uu.se>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: "eliminate warn_on_slowpath()" change causes many gcc-3.2.3 warnings

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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