New Silicon Insider Article

Article: Sizing up the Super Heavyweights
By: Arun Ramakrishnan (arunr.delete@this.sgi.com), October 23, 2004 1:47 pm
Room: Moderated Discussions
David Kanter (dkanter@realworldtech.com) on 10/23/04 wrote:
---------------------------
>Paul DeMone (pdemone@igs.net) on 10/22/04 wrote:
>---------------------------
>>Arun Ramakrishnan (arunr@sgi.com) on 10/22/04 wrote:
>>---------------------------
>>[..]
>>>Why would the L2 I-cache be about 4 times the size of the L2 D-cache ?
>>>I always thought that MPU desginers would try to cut the latency of access to user
>>>data much more than the intruction stream itself.
>
>Well, if you think about it, a large Icache is far more important. An ICache miss
>means that you are wasting many cycles, no matter how the data cache performs.
>In contrast, if the data cache performs poorly, then a context switch producing
>hits in the ICache could still provide useful work.
>
>>IA-64 has low code density. A 1.0 MB/256KB IPF design
>>has similar instruction/data balance as roughly a 512
>>KB/256 KB RISC design. A bigger L2 icache also reduces
>>average instruction stream bandwidth demand on the L3.
>
>Actually, I was thinking along different lines. Andy Glew and I talked about this
>briefly, but there was a paper out of UW-Madison that indicated that the 'working
>set' for a database is ~1MB for ICache. I do not know which architecture this was, but I suspect it was Alpha or x86...
>
>Unfortunately, I do not recall the author of the paper, but it was quite interesting.
>
>>>Would this have something to do with the fact that two coarse grained threads on
>>>the core need to fed rapidly in order to keep the CMP efficiency high ?
>>
>>Yep, that's probably the biggest reason. I also suspect
>>it will give a noticable boost to IA-32 EL performance.
>
>Why do you think it will give a particular boost to IA32EL? I am curious here.
>My initial thought was that they wanted to provide higher database performance.
>
>David


Thanks David for your explanation.I always looked from a benchmark perspective when data was not getting fast enough to codes and most the functional units were sitting idle :)

Another interesting point brought forward by all of you is IA32EL performance.
At present,the IA32 performance is about 70-75% of native speeds with FP heavy ia32 codes(which are not that many:))
enjoying the boost in IA64 fp performance.
But still,i dont think it would ever become competitive with a Opteron at all.
I guess the compatibility with IA32 is the motive here rather than performance.

Would IA32EL performance on the Montecito enjoy a big enough boost to become at least 80% of native x86 cpus like Opteron ? That would be nice to have one but given the speed of x86 cpus touching 3+GHz now,the IA32EL performance looks rather weak.

As a side note,the largest application running on IA64 is database :) So i would not be surprised if Intel was helping them out.

Cheers
Arun


Cheers,
Arun
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New Silicon Insider ArticleDavid Kanter2004/10/11 05:43 AM
  Good read. Thanks again Paul. (NT)Michael Menietti2004/10/11 06:36 AM
  New Silicon Insider ArticleSingh, S.R.2004/10/11 06:44 AM
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  New Silicon Insider Articletecate2004/10/11 09:52 AM
  core size: x86 vs IPFanonymous2004/10/11 11:43 AM
    Good Question. (NT)Chuck2004/10/12 08:22 AM
    core size: x86 vs IPFMichael S2004/10/12 10:53 AM
    K8 core size 52mm^2IlleglWpns2004/10/12 12:15 PM
    core size: x86 vs IPFPaul DeMone2004/10/12 01:10 PM
  New Silicon Insider ArticleJS2004/10/13 02:42 AM
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  New Silicon Insider ArticleArun Ramakrishnan2004/10/22 08:48 AM
    New Silicon Insider ArticlePaul DeMone2004/10/22 10:38 AM
      New Silicon Insider ArticleDavid Kanter2004/10/22 11:04 PM
        New Silicon Insider ArticlePaul DeMone2004/10/23 06:02 AM
        New Silicon Insider ArticleArun Ramakrishnan2004/10/23 01:47 PM
      New Silicon Insider ArticleMichael S2004/10/23 11:38 AM
        New Silicon Insider ArticlePaul DeMone2004/10/23 01:10 PM
          New Silicon Insider ArticleMichael S2004/10/23 01:40 PM
  Do I see a flaw here?IntelUser20002004/10/27 05:43 PM
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      Frequency is different for startersIntelUser2004/10/27 06:28 PM
        Frequency is different for startersPaul DeMone2004/10/27 07:49 PM
          Frequency is different for startersIntelUser20002004/10/27 08:45 PM
  New Silicon Insider ArticleIntelUser20002004/11/01 10:13 AM
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      New Silicon Insider ArticleDavid Kanter2004/11/05 08:44 AM
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