From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [RFC] speeding up the stat() family of system calls...
Date: Thu, 26 Dec 2013 22:09:30 -0800
Message-ID: <52BD199A.8070607@zytor.com>
References: <CA+55aFxZ2u+M72u3HSD7TVY2+WRRi27pYC=_4Wawr5y1m8DfnQ@mail.gmail.com>	<20131224204625.GB20471@gmail.com> <CA+55aFzPBdbfKovMT8Edr4SmE2_=+OKJFac9XW2awegogTkVTA@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Cc: Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Al Viro <viro@zeniv.linux.org.uk>,
	the arch/x86 maintainers <x86@kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <CA+55aFzPBdbfKovMT8Edr4SmE2_=+OKJFac9XW2awegogTkVTA@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

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