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> Moore’s law is far from over and multithreading is not the answer. Wut? We hit the power wall back in 2004. There was a little bit of optimization around the

by Kamq 3y ago

> Moore’s law is far from over and multithreading is not the answer. Wut? We hit the power wall back in 2004. There was a little bit of optimization around the memory wall and ilp wall afterwards, but really, cores haven't gotten faster since. It's been all about being able to cram more cores in since then, which implies at least multi-threading, but multi-processing is basically required to get the most out of a cpu these days.

ikura 3y ago
Moore's law is "the observation that the number of transistors in an integrated circuit doubles about every two years". For a while clock speed was a proxy for that metric, but it's not the 'law' itself.
- Kamq 3y ago
  Yeah, but today number of cores is the rough proxy for that metric. How do you operate in that world if "multithreading isn't the answer"?
  - samus 3y ago
    Modern CPUs contain a lot more computing units than cores. For a while, hyperthreading was thought to be a useful way to make use of them. More recently, people have turned to advanced instruction sets like SSE and AVX.
    - FridgeSeal 3y ago
      Those things aren’t mutually exclusive. Also firstly, I suspect there’s more “low hanging fruit” in making more software make use of more cores. We’re increasingly getting better languages, tooling and libs for multi threading stuff, and it’s far more in the realm of your average developer than writing SIMD compatible code and making sure your code can pipeline properly.
      - samus 3y ago
        Threads are of course appropriate to implement high-level concurrency and parallelism. But for fine-grained parallelism, they are unwieldy and have high overhead. Spreading an algorithm across multiple threads makes it more difficult for an optimizing compiler to find opportunities for SIMD optimization. Similarly to how modern languages make it easier to safely use threads, runtimes also make it easier to take advantage of SIMD optimizations. For example, recently a SIMD-optimized sorting algorithm was included in OpenJDK. Apart from that, SIMD is way less brittle at runtime than GPUs and other accelerators.

by Kamq 3y ago

ikura 3y ago

Moore's law is "the observation that the number of transistors in an integrated circuit doubles about every two years". For a while clock speed was a proxy for that metric, but it's not the 'law' itself.

Kamq 3y ago
Yeah, but today number of cores is the rough proxy for that metric. How do you operate in that world if "multithreading isn't the answer"?
- samus 3y ago
  Modern CPUs contain a lot more computing units than cores. For a while, hyperthreading was thought to be a useful way to make use of them. More recently, people have turned to advanced instruction sets like SSE and AVX.
  - FridgeSeal 3y ago
    Those things aren’t mutually exclusive. Also firstly, I suspect there’s more “low hanging fruit” in making more software make use of more cores. We’re increasingly getting better languages, tooling and libs for multi threading stuff, and it’s far more in the realm of your average developer than writing SIMD compatible code and making sure your code can pipeline properly.
    - samus 3y ago
      Threads are of course appropriate to implement high-level concurrency and parallelism. But for fine-grained parallelism, they are unwieldy and have high overhead. Spreading an algorithm across multiple threads makes it more difficult for an optimizing compiler to find opportunities for SIMD optimization. Similarly to how modern languages make it easier to safely use threads, runtimes also make it easier to take advantage of SIMD optimizations. For example, recently a SIMD-optimized sorting algorithm was included in OpenJDK. Apart from that, SIMD is way less brittle at runtime than GPUs and other accelerators.