Barcelona vs Core2

By: David Kanter (dkanter.delete@this.realworldtech.com), May 16, 2007 11:06 am
Room: Moderated Discussions
Vincent Diepeveen (diep@xs4all.nl) on 5/16/07 wrote:
---------------------------
>David Kanter (dkanter@realworldtech.com) on 5/16/07 wrote:
>---------------------------
>>Vincent Diepeveen (diep@xs4all.nl) on 5/13/07 wrote:
>>
>>>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.
>>
>>Yes and the concord can fly faster than a 787...oh wait, no, it doesn't fly anymore : )
>>
>>I have yet to find any code with > 2 uops/cycle, so Intel's 4th issue/execute/retire
>>slot really doesn't help all that much. Nobody consistently has IPC=3...
>>
>>It helps for clearing queuing up, but it really isn't that important. What IPC does your code get on Core2 anyways?
>>DK
>
>It really doesn't matter what software i look to that i >wrote myself, they all
>profit bigtime from a 4th execution unit.

I really don't think that's true.

>Your math model might need a more realistic approach.
>
>The total speed of your software gets dominated by the >average IPC you can get,
>yet consistently getting above 2.0 is total unnecessary to >already profit from the possibility to execute 4 a cycle.
>
>Let's show in a sample calculation how relevant your remark >is that it should be 'consistently higher' than ipc 3.0.
>
>Let's use an example where a program in 80% of the code >cannot profit from moving
>from 3 to 4 integer units, that means that if 20% does >profit.
>
>That 20% gets a speedup of 33%.
>
>Your total program speedup then is:
>
>100% - 80% - (20 * 3 / 4 ) = 5%
>
>So even for software that hardly can need a 4th unit, >already can easily get a speedup of 5% from it.
>
>In reality however, many instructions from intel are dead >slow, so the observed
>speedup at chips that can retire 4 instructions a cycle is >far bigger than that 5%.

You're just making up arbitrary numbers and guessing about this. What would convince me that a 4th pipeline really matters is someone profiling their software and telling me:

In 5% of all cycles, we retired 4 uops.

Again, what IPC does your code achieve? In looking at modern games, I have yet to see an IPC greater than 1.5.

David
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Barcelona optimization guidemas2007/05/10 06:43 AM
  Barcelona optimization guideLinus Torvalds2007/05/10 09:00 AM
    Barcelona optimization guideRob Thorpe2007/05/10 09:23 AM
      Barcelona optimization guideLinus Torvalds2007/05/10 09:42 AM
        Barcelona optimization guideRob Thorpe2007/05/11 08:22 AM
          Barcelona optimization guideDavid Kanter2007/05/11 04:17 PM
            Barcelona optimization guideLinus Torvalds2007/05/11 04:30 PM
            Barcelona optimization guideanonymous2007/05/11 10:29 PM
              Barcelona optimization guideanonymous2007/05/12 06:47 AM
              Barcelona optimization guidehobold2007/05/14 04:30 AM
        Barcelona optimization guideAndreas Kaiser2007/05/12 08:32 AM
  Barcelona optimization guideVincent Diepeveen2007/05/13 04:20 AM
    Barcelona optimization guideEduardoS2007/05/13 06:01 AM
      Barcelona optimization guideVincent Diepeveen2007/05/13 08:18 AM
        Barcelona optimization guideMichael S2007/05/13 09:03 AM
        Barcelona optimization guideEduardoS2007/05/13 09:30 AM
        Barcelona optimization guideDresdenboy2007/05/14 07:18 AM
          Barcelona optimization guideVincent Diepeveen2007/05/16 01:36 AM
            Barcelona optimization guideEduardoS2007/05/16 05:57 AM
              Barcelona optimization guideVincent Diepeveen2007/05/16 08:51 AM
        Barcelona optimization guideDavid Kanter2007/05/16 03:13 AM
          Barcelona vs Core2 Vincent Diepeveen2007/05/16 05:35 AM
            Barcelona vs Core2 David Kanter2007/05/16 11:06 AM
            Barcelona vs Core2 EduardoS2007/05/16 11:41 AM
              Barcelona vs Core2 David Kanter2007/05/16 11:53 AM
                Barcelona vs Core2 EduardoS2007/05/16 12:37 PM
                  Barcelona vs Core2 David Kanter2007/05/16 01:43 PM
                    Barcelona vs Core2 EduardoS2007/05/16 03:32 PM
                    Barcelona vs Core2 Gabriele Svelto2007/05/17 05:38 AM
          Barcelona optimization guideanonymous2007/05/16 07:13 PM
            Barcelona optimization guideMichael S2007/05/17 04:26 AM
              Barcelona optimization guideanonymous2007/05/17 05:23 PM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell avocado?