From: "H. Peter Anvin" <hpa@zytor.com>
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
Date: Sat, 17 Jan 2009 15:40:06 -0800 [thread overview]
Message-ID: <49726C56.6080905@zytor.com> (raw)
In-Reply-To: <alpine.LFD.2.00.0901181032350.3006@localhost.localdomain>
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.
next prev parent reply other threads:[~2009-01-17 23:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-17 15:19 "eliminate warn_on_slowpath()" change causes many gcc-3.2.3 warnings Mikael Pettersson
2009-01-17 16:18 ` Ingo Molnar
2009-01-17 20:01 ` H. Peter Anvin
2009-01-17 20:44 ` Kyle McMartin
2009-01-17 20:57 ` Kyle McMartin
2009-01-17 21:07 ` H. Peter Anvin
2009-01-17 21:38 ` Kyle McMartin
2009-01-17 23:37 ` Linus Torvalds
2009-01-17 23:40 ` H. Peter Anvin [this message]
2009-01-18 0:01 ` Linus Torvalds
2009-01-18 0:10 ` H. Peter Anvin
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