Barcelona optimization guide

By: Dresdenboy (, May 14, 2007 8:18 am
Room: Moderated Discussions
Vincent Diepeveen ( on 5/13/07 wrote:
>EduardoS ( on 5/13/07 wrote:
>>The latency is 4 cycles for the lower 64 bits, 5 for the upper, comparing that upper to other processors:
>>K-8: 5 cycles
>>C2D: 7 cycles
>>P4E: 11 cycles
>>Multiply is a complex instruction, 5 cycles is ok.
>So if your car can drive at most at 100 KM/h,
>then it is an ok driving speed considering
>T-ford getting a speed at most of 40 KM/h ??

But throughput is still 1/cycle for 64 bit muls and 0.5/cycle for 128 bit muls. Problem is only, that the result isn't available that quickly, but OOO execution will manage to hide that to some extent.

>>>I was under the probably wrong misconception that it would be able to execute 4 instructions a cycle at integer area.
>>>When i read manual correct i deduce it's executing 3 instructions maximum a cycle.
>>>So Intel has bigger surplus potential of 33% for good programmers, did i read that
>>>correct, or am i wrong there and is core2 not having 4 integer units either?
>>Core 2 have 4 decoders (up to 5 instructions per clock with macro-fusion) but only
>>3 integer units and can retire only 4 uOPs per cycle, Barcelona isn't too far behind, if any.
>If core2 can retire 4 uops per cycle and barcelona can retire 3 uops a cycle i
>understand, then core2 can blow that barcelona core completely away. That's 33% faster speed.

As already said, µOps/MacroOps are different. If an x86 instruction contains complex memory operand addresses then C2D has to create at least 2 µops, while already K8 created only 1 MacroOp then. So 3 MacroOps/cycle mean up to 6 µOps/cycle, but without any explicitly fused ops.
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TopicPosted ByDate
Barcelona optimization guidemas2007/05/10 07:43 AM
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  Barcelona optimization guideVincent Diepeveen2007/05/13 05:20 AM
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      Barcelona optimization guideVincent Diepeveen2007/05/13 09:18 AM
        Barcelona optimization guideMichael S2007/05/13 10:03 AM
        Barcelona optimization guideEduardoS2007/05/13 10:30 AM
        Barcelona optimization guideDresdenboy2007/05/14 08:18 AM
          Barcelona optimization guideVincent Diepeveen2007/05/16 02:36 AM
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        Barcelona optimization guideDavid Kanter2007/05/16 04:13 AM
          Barcelona vs Core2 Vincent Diepeveen2007/05/16 06:35 AM
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            Barcelona optimization guideMichael S2007/05/17 05:26 AM
              Barcelona optimization guideanonymous2007/05/17 06:23 PM
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