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On Wednesday 14 September 2005 09:48, Zwane Mwaikambo wrote: > 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 ?! add/sub doesn't modify "only one bit in eflags", it modifies all. In fact, it's dec/inc which does not modify all bits. It doesn't touch 'carry' bit (IIRC). If inc/dec is slower on P4, it must be just another P4 quirk. > increased code size with add/sub. > > But i've never benchmarked all of this ;) I don't even have one to test this. -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||
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