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And yet... the world keeps proving Intel and AMD wrong on this premise with highly efficient Arm parts. While sure, there's bound to be improvements to make on

by bfrog 1y ago

And yet... the world keeps proving Intel and AMD wrong on this premise with highly efficient Arm parts. While sure, there's bound to be improvements to make on x86 ultimately its a variable length opcode encoding with a complex decoder path. If nothing else, this is likely a significant issue in comparison to the nicely word aligned op code encoding arm has and surely given apples to apples core designs, the opcode decoding would be a deciding factor.

tinktank 1y ago
PPA results comparing x86 to ARM say otherwise; take a look at Ryzen's embedded series and Intel's latest embedded cores.
- bfrog 1y ago
  Have they reached apple m level of performance/watt after half a decade of the apple m parts being out yet? Do either AMD or Intel beat Apple in any metric in mobile?
  - deleted 1y ago
    [deleted]
  - tinktank 1y ago
    Yes and yes - again, go look at the published results.
    - bfrog 1y ago
      I have, the m4 is significantly ahead by any measure I’ve seen, with snapdragon just behind. https://www.xda-developers.com/tested-apple-m4-vs-intel-lunar-lake-snapdragon-x-elite/ https://www.xda-developers.com/tested-apple-m4-vs-intel-luna...
      - Jensson 1y ago
        The m4 is not the same fab technology so not comparable. If you want to discuss the validity of some CPU architecture it needs to be between comparable fab technology, M4 being a generation ahead there makes the comparison unfair. If you compare like to like the difference almost completely disappears.
        bfrog 1y ago
        You mean how they all use tsmc n3 and the two arm parts still beat out lunar lake? It’s not like a whole generational node behind here. I get they aren’t the exact same process node but still.
        bfrog 1y ago
        X elite uses an older node than lunar lake and does better
    - daneel_w 1y ago
      No they haven't.
ch_123 1y ago
> its a variable length opcode encoding with a complex decoder path In practice, the performance impact of variable length encoding is largely kept in check using predictors. The extra complexity in terms of transistors is comparatively small in a large, high-performance design. Related reading: https://patents.google.com/patent/US6041405A/en https://patents.google.com/patent/US6041405A/en https://web.archive.org/web/20210709071934/https://www.anandtech.com/show/16762/an-anandtech-interview-with-jim-keller-laziest-person-at-tesla https://web.archive.org/web/20210709071934/https://www.anand...
- devnullbrain 1y ago
  Jim Keller has a storied career in the x86 world, it isn't surprising he speaks fondly of it. Regardless: >So fixed-length instructions seem really nice when you're building little baby computers, but if you're building a really big computer, to predict or to figure out where all the instructions are, it isn't dominating the die. So it doesn't matter that much. Well, efficiency advantages are the domain of little baby computers. Better predictors give you deeper pipelines without stalls which give you higher clock speeds - higher wattages
deleted 1y ago
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by bfrog 1y ago

tinktank 1y ago

PPA results comparing x86 to ARM say otherwise; take a look at Ryzen's embedded series and Intel's latest embedded cores.

bfrog 1y ago
Have they reached apple m level of performance/watt after half a decade of the apple m parts being out yet? Do either AMD or Intel beat Apple in any metric in mobile?
- deleted 1y ago
  [deleted]
- tinktank 1y ago
  Yes and yes - again, go look at the published results.
  - bfrog 1y ago
    I have, the m4 is significantly ahead by any measure I’ve seen, with snapdragon just behind. https://www.xda-developers.com/tested-apple-m4-vs-intel-lunar-lake-snapdragon-x-elite/ https://www.xda-developers.com/tested-apple-m4-vs-intel-luna...
    - Jensson 1y ago
      The m4 is not the same fab technology so not comparable. If you want to discuss the validity of some CPU architecture it needs to be between comparable fab technology, M4 being a generation ahead there makes the comparison unfair. If you compare like to like the difference almost completely disappears.
      - bfrog 1y ago
        You mean how they all use tsmc n3 and the two arm parts still beat out lunar lake? It’s not like a whole generational node behind here. I get they aren’t the exact same process node but still.
      - bfrog 1y ago
        X elite uses an older node than lunar lake and does better
  - daneel_w 1y ago
    No they haven't.

ch_123 1y ago

> its a variable length opcode encoding with a complex decoder path In practice, the performance impact of variable length encoding is largely kept in check using predictors. The extra complexity in terms of transistors is comparatively small in a large, high-performance design. Related reading: https://patents.google.com/patent/US6041405A/en https://patents.google.com/patent/US6041405A/en https://web.archive.org/web/20210709071934/https://www.anandtech.com/show/16762/an-anandtech-interview-with-jim-keller-laziest-person-at-tesla https://web.archive.org/web/20210709071934/https://www.anand...

devnullbrain 1y ago
Jim Keller has a storied career in the x86 world, it isn't surprising he speaks fondly of it. Regardless: >So fixed-length instructions seem really nice when you're building little baby computers, but if you're building a really big computer, to predict or to figure out where all the instructions are, it isn't dominating the die. So it doesn't matter that much. Well, efficiency advantages are the domain of little baby computers. Better predictors give you deeper pipelines without stalls which give you higher clock speeds - higher wattages

deleted 1y ago

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