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

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Message-ID: <52BE0D89.3080405@zytor.com>
Date:	Fri, 27 Dec 2013 15:30:17 -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 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.

	-hpa


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