From: Denis Vlasenko <vda@ilport.com.ua>
To: Margit Schubert-While <margitsw@t-online.de>
Cc: chriswhite@gentoo.org, linux-kernel@vger.kernel.org,
zwane@arm.linux.org.uk
Subject: Re: 2.6.13/14 x86 Makefile - Pentiums penalized ?
Date: Wed, 14 Sep 2005 10:54:08 +0300 [thread overview]
Message-ID: <200509141054.08975.vda@ilport.com.ua> (raw)
In-Reply-To: <5.1.0.14.2.20050914092308.025ca630@pop.t-online.de>
>
> In the Intel Architecture Optimization document it specifically states
> (Chapter 2.6) :
> "Avoid instructions that unnecessarily introduce dependence-related
> stalls: inc and dec instructions, .....".
> And again on page 2-11 :
> "The inc and dec instructions should always be avoided. Using add and
> sub instructions instead avoids data dependence and improves performance".
> And on page 2-71 :
> "The inc and dec instructions modify only a subset of flags in the flag
> register.
> This creates a dependence on all previous writes of the flag register.
> This is especially problematic when these instructions are on the critical
> path because they are used to change an address for a load on which
> many other instructions depend. "
Well it sounds dramatic but in reality I doubt it is such a big deal.
Anyone to bench it?
> However, the kernel include and arch have a liberal sprinkling of inc/dec,
> and AFAICT some of these in hot-path.
--
vda
next prev parent reply other threads:[~2005-09-14 7:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-13 6:04 Margit Schubert-While
2005-09-14 5:14 ` Chris White
2005-09-14 6:48 ` Zwane Mwaikambo
2005-09-14 6:59 ` Denis Vlasenko
2005-09-14 7:21 ` Zwane Mwaikambo
2005-09-14 7:51 ` Denis Vlasenko
2005-09-14 7:48 ` Margit Schubert-While
2005-09-14 7:54 ` Denis Vlasenko [this message]
2005-09-14 7:02 ` Margit Schubert-While
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