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Nineties probably wants its CISC vs RISC fight back. Nowadays it just doesn't matter, because CPUs translate ISA into whatever they please. Cache and out of o

Nineties probably wants its CISC vs RISC fight back. Nowadays it just doesn't matter, because CPUs translate ISA into whatever they please. Cache and out of order buffers (speculation) is what is behind latest security issues.

snvzz 9y ago
>Nowadays it just doesn't matter, because CPUs translate ISA to whatever they please. Doing that comes at a cost, which compounds the complexity already added by merit of being CISC in the first place.
- vardump 9y ago
  Larger code size is not for free either. Besides, this translation layer is not a major source of complexity anymore. Even instruction decoding in x86 is not a big deal anymore.
  - microcolonel 9y ago
    I think you somewhat underestimate the complexity introduced by decoding x86, and working with the resulting μ-ops.
  - snvzz 9y ago
    >Larger code size is not for free either. What larger code size? RISC-V is no worse than x86-64. Refer to: https://riscv.org/wp-content/uploads/2016/07/Tue1130celio-fusion-finalV2.pdf https://riscv.org/wp-content/uploads/2016/07/Tue1130celio-fu...
    - vardump 9y ago
      That's a nice property for sure. Typically RISC ISAs have had larger code size. Being a new ISA, RISC-V does have an advantage of being able to learn from past mistakes.
      - deleted 9y ago
        [deleted]
      - snvzz 9y ago
        Simple vs Complex, but same code size. An easy win for simple. It's very nice, indeed. Unlike the established RISC ISAs, this one's created with decades of RISC (and CISC) experience to draw from. I'd of course still have my doubts whether this is going to draw any traction, if it wasn't for the list of RISC-V Foundation members.
ant6n 9y ago
> Cache and out of order buffers (speculation) is what is behind latest security issues. That's one way to look at it. Another is that opaque CPU designs are a big issue (at least for meltdown, which is a bug; spectre is more of a broken design philosophy).
dbcurtis 9y ago
Today there is a benefit from the higher code density of CISC. 1. Less memory bandwith expended moving instructuons into I-cache. 2. Less die area spent on I-cache per unit of "code functionality", however you mesure that. RISC only made sense when logic cycle times, memory cycle times, and I/O cycle times were at rough parity.
- snvzz 9y ago
  If you read the rest of the thread, you'd find that both of your points are moot, as RISC-V code density is no worse than x86-64. As for your claims on RISC not making sense, I'll just say it makes more sense than ever, as complexity leads to issues, which could affect security, and security is important in the present networked world.

snvzz 9y ago

>Nowadays it just doesn't matter, because CPUs translate ISA to whatever they please. Doing that comes at a cost, which compounds the complexity already added by merit of being CISC in the first place.

vardump 9y ago
Larger code size is not for free either. Besides, this translation layer is not a major source of complexity anymore. Even instruction decoding in x86 is not a big deal anymore.
- microcolonel 9y ago
  I think you somewhat underestimate the complexity introduced by decoding x86, and working with the resulting μ-ops.
- snvzz 9y ago
  >Larger code size is not for free either. What larger code size? RISC-V is no worse than x86-64. Refer to: https://riscv.org/wp-content/uploads/2016/07/Tue1130celio-fusion-finalV2.pdf https://riscv.org/wp-content/uploads/2016/07/Tue1130celio-fu...
  - vardump 9y ago
    That's a nice property for sure. Typically RISC ISAs have had larger code size. Being a new ISA, RISC-V does have an advantage of being able to learn from past mistakes.
    - deleted 9y ago
      [deleted]
    - snvzz 9y ago
      Simple vs Complex, but same code size. An easy win for simple. It's very nice, indeed. Unlike the established RISC ISAs, this one's created with decades of RISC (and CISC) experience to draw from. I'd of course still have my doubts whether this is going to draw any traction, if it wasn't for the list of RISC-V Foundation members.

ant6n 9y ago

> Cache and out of order buffers (speculation) is what is behind latest security issues. That's one way to look at it. Another is that opaque CPU designs are a big issue (at least for meltdown, which is a bug; spectre is more of a broken design philosophy).

dbcurtis 9y ago

Today there is a benefit from the higher code density of CISC. 1. Less memory bandwith expended moving instructuons into I-cache. 2. Less die area spent on I-cache per unit of "code functionality", however you mesure that. RISC only made sense when logic cycle times, memory cycle times, and I/O cycle times were at rough parity.

snvzz 9y ago
If you read the rest of the thread, you'd find that both of your points are moot, as RISC-V code density is no worse than x86-64. As for your claims on RISC not making sense, I'll just say it makes more sense than ever, as complexity leads to issues, which could affect security, and security is important in the present networked world.