linux-kernel - Re: [PATCH] x86: make use of inc/dec conditional

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Message-Id: <4A8BE0BE0200007800010890@vpn.id2.novell.com>
Date:	Wed, 19 Aug 2009 10:23:42 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>
Cc:	<mingo@...e.hu>, "Peter Zijlstra" <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86: make use of inc/dec conditional

>>> Thomas Gleixner <tglx@...utronix.de> 19.08.09 11:06 >>>
>You still do not tell on which machines the INC/DEC instructions
>should be avoided and why. GCC avoiding it is not a convincing
>argument.

On Pentium4 (Prescott/Nocona) inc/dec not modifying the carry flag cause
an extra instruction dependency on EFLAGS, and hence extra latency in
when the instruction can be scheduled for execution.

Jan

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