Re: 2.6.13/14 x86 Makefile - Pentiums penalized ?

[Zwane Mwaikambo]

On Wed, 14 Sep 2005, Chris White wrote:

> That's correct, gcc 3.4 started the -mtune flag.  Chances are if you really 
> want the -mtune optimizations you're going to have to upgrade to gcc 3.4 or 
> greater.
> 
> > This, of course, heavily penalizes P4's (the notorious inc/dec).
> 
> Are you referring to cpu cycle counts?  Is there certain code that causes the 
> kernel to perform that unfavorably by a large scale?

It's documented as being suboptimal to use inc/dec due to it modifying all 
of eflags resulting in dependency related stalls. add/sub only modifies 
one bit of eflags so is more optimal. However there is a problem of 
increased code size with add/sub.

But i've never benchmarked all of this ;)

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