linux-kernel - Re: [RFC] speeding up the stat() family of system calls...

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Message-ID: <52BD199A.8070607@zytor.com>
Date:	Thu, 26 Dec 2013 22:09:30 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] speeding up the stat() family of system calls...

On 12/26/2013 11:00 AM, Linus Torvalds wrote:
> 
> Interestingly, looking at the cp_new_stat() profiles, the games we
> play to get efficient range checking seem to actually hurt us. Maybe
> it's the "sbb" that is just expensive, or maybe it's turning a (very
> predictable) conditional branch into a data dependency chain instead.
> Or maybe it's just random noise in my profiles that happened to make
> those sbb's look bad.
> 

Much to my surprise, this patch adds almost 10K of text to an
"allyesconfig" build.  I wouldn't have expected it.  I'll look at it
some more tomorrow.

	-hpa


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