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

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Date:	Sun, 12 Jan 2014 18:46:07 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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...


* H. Peter Anvin <hpa@...or.com> wrote:

> On 12/26/2013 10:09 PM, H. Peter Anvin wrote:
> > 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.
> 
> Mystery solved... it is all code added by gcov &c because a new 
> (inline) function is added to the code base.  So it is fluff, not 
> real.

Yeah, defconfig builds are better for size comparisons, at least on 
x86 they are distro-config derived so a lot more relevant to real life 
than allyesconfig or allmodconfig.

Thanks,

	Ingo
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