Author: Tom Kerrigan
Date: 01:45:42 02/12/03
Go up one level in this thread
On February 12, 2003 at 01:58:36, Matt Taylor wrote: >Branch prediction is mostly unrelated to OOOE. The IA-64 does have branch >prediction. It does not have OOOE. Of course it's related. Compilers have to rely on static branch prediction (80% accuracy) if they're going to effectively advance instructions before branches. >On a final note, the Athlon has a 72-entry integer scheduler and IIRC a 36-entry >FP scheduler. Athlon can therefore see up to 72 instructions ahead. (Remember -- >1 DirectPath instruction translates 1:1 with a macro-op, or this is the >impression I get from the docs anyway.) The compiler can still see futher. Indeed. It's a shame only IA-64 chips run compiled code... oh, wait... >No. Predication is the IA-64's answer to branch prediction. Predication is >completely unrelated to OOOE. What, exactly, do you think the point of predication is, then? It's to allow instructions to execute before the condition is determined, in other words, out of order. (Or at least in order without being dependent.) If you think predicated instructions are only executed after the condition is determined, then what is the difference between a "predicated branch" and a normal branch, besides some extra instructions? >Dr. Hyatt's figures "in practice" still show an 1 GHz McKinley 4 times faster >clock-for-clock than a Pentium 4. And every other SPEC program shows that "in practice" McKinley is clearly slower than a P4. >The last two questions are more an answer to the question, "How will the IA-64 >scale?" The question I am answering (and the question originally asked) is, "How >fast currently is the IA-64 compared to the IA-32/AA-64 in Chess?" Your confusion about the original question continues. Somebody asked what the relative advantages of x86-64 and IA-64 are. It had nothing to do with IA-32. I have no way to prove this because the post seems to be gone, but I also distinctly remember writing a post with lists of advantages for each chip and not mentioning anything about IA-32. As for all the extraneous trivia you provided about the chips in question, don't bother. I already know it. -Tom
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