Messages in this thread | | | Date | Tue, 13 Sep 2005 23:48:22 -0700 (PDT) | From | Zwane Mwaikambo <> | Subject | Re: 2.6.13/14 x86 Makefile - Pentiums penalized ? |
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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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