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

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Message-ID: <alpine.LFD.2.00.0908191150340.3361@localhost.localdomain>
Date:	Wed, 19 Aug 2009 11:56:41 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jan Beulich <JBeulich@...ell.com>
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

On Wed, 19 Aug 2009, Jan Beulich wrote:

> >>> 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.

Do we really care that much about those electronic heaters which are
scheduled for darwinistic extinction since their introduction ?

Thanks,

	tglx
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