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Why is AVX-512 disabled on golden cove? Seems odd for them to work so hard on the architecture and these optimizations only to remove it. Is there a specific

Why is AVX-512 disabled on golden cove? Seems odd for them to work so hard on the architecture and these optimizations only to remove it. Is there a specific reason, such as power consumption or heat?

monocasa 4y ago
At the last minute they got strapped to efficiency cores (Gracemont) that didn't implement AVX-512, and the schedulers of OSes they cared about running couldn't handle heterogeneous core features. Because of that they probably didn't finish verification of AVX-512 on the Golden Cove cores.
- nosebear 4y ago
  I bought my i5-12500 (that has no Gracemont cores) just when it came out. Linux reported all kinds of AVX-512 extensions and I could transcode video with Handbrake using AVX-512 without any problems. Later on Intel pushed a microcode update, and now my CPU doesn't have AVX-512 enabled anymore.
  - dmitrygr 4y ago
    microcode updates are volatile, you can rollback your microcode package in your distro and get the capability back. Some BIOSes also apply microcode. If you updated your BIOS, roll that back instead.
    - nosebear 4y ago
      I updated my BIOS, and I'd rather have security fixes than AVX-512 that I don't really need because all I do with this machine is surfing the internet and watching movies. Thanks for the tip nevertheless! I was just referring to OP who said that Intel probably didn't verify AVX-512 thoroughly, because it seems they did.
      - justinjlynn 4y ago
        It's amazing to me that Intel can - without being held accountable, and for obvious strategic commercial gain - disable vital, working functionality in products they've already sold through the use of combined updates which are otherwise legitimately meant to address things about their products which are dangerously broken. Apply them and lose the function or be vulnerable and unstable. They can't keep getting away with this, and yet, they do.
        wmf 4y ago
        In this case AVX-512 was never advertised so Intel feels justified in removing an "easter egg".
        justinjlynn 4y ago
        I mean, most vehicle manufacturers don't advertise that their transmissions have a 'reverse' gear but it doesn't mean they can just remove it using a software update...
berkut 4y ago
Because the 'efficiency' cores are actually optimised for silicon area efficiency (and not just low power usage, like is generally the case with things like ARM big.LITTLE setups), and AVX-512 native takes up a lot of silicon space on the chips Intel has implemented it for. And because it's not clear how OS schedulers could nicely switch on-the-fly between cores with different instruction set capabilities, it's essentially not use-able.
- moonchild 4y ago
  > it's not clear how OS schedulers could nicely switch on-the-fly between cores with different instruction set capabilities It is a software problem, and it could have been solved with software. It was simply assumed a priori that it couldn't be solved, so no one bothered to try.
  - wmf 4y ago
    Or they talked to Microsoft who said it would take years to add that feature.
    - undersuit 4y ago
      Or they talked with Microsoft who refused to add it to anything but Windows 11. Or maybe they can't handle it because of some difficiency in their Linux ports. The thing is it is possible and Intel knew for years that the E-cores wouldn't have AVX512.
    - moonchild 4y ago
      Let it take years, then. Leaving it disabled in the bios by default is one thing, and a rather reasonable one at that. Fusing it off is quite another.
  - Twirrim 4y ago
    This isn't a new decision, it came out a few years ago that you'd end up with disparate instruction sets between the main and efficiency cores, and they got warned it would be a problem. Their disabling of the instructions to avoid it came about as a response. Both Microsoft and Linux devs warned them about the difficulties it'd present.

monocasa 4y ago

At the last minute they got strapped to efficiency cores (Gracemont) that didn't implement AVX-512, and the schedulers of OSes they cared about running couldn't handle heterogeneous core features. Because of that they probably didn't finish verification of AVX-512 on the Golden Cove cores.

nosebear 4y ago
I bought my i5-12500 (that has no Gracemont cores) just when it came out. Linux reported all kinds of AVX-512 extensions and I could transcode video with Handbrake using AVX-512 without any problems. Later on Intel pushed a microcode update, and now my CPU doesn't have AVX-512 enabled anymore.
- dmitrygr 4y ago
  microcode updates are volatile, you can rollback your microcode package in your distro and get the capability back. Some BIOSes also apply microcode. If you updated your BIOS, roll that back instead.
  - nosebear 4y ago
    I updated my BIOS, and I'd rather have security fixes than AVX-512 that I don't really need because all I do with this machine is surfing the internet and watching movies. Thanks for the tip nevertheless! I was just referring to OP who said that Intel probably didn't verify AVX-512 thoroughly, because it seems they did.
    - justinjlynn 4y ago
      It's amazing to me that Intel can - without being held accountable, and for obvious strategic commercial gain - disable vital, working functionality in products they've already sold through the use of combined updates which are otherwise legitimately meant to address things about their products which are dangerously broken. Apply them and lose the function or be vulnerable and unstable. They can't keep getting away with this, and yet, they do.
      - wmf 4y ago
        In this case AVX-512 was never advertised so Intel feels justified in removing an "easter egg".
        justinjlynn 4y ago
        I mean, most vehicle manufacturers don't advertise that their transmissions have a 'reverse' gear but it doesn't mean they can just remove it using a software update...

berkut 4y ago

Because the 'efficiency' cores are actually optimised for silicon area efficiency (and not just low power usage, like is generally the case with things like ARM big.LITTLE setups), and AVX-512 native takes up a lot of silicon space on the chips Intel has implemented it for. And because it's not clear how OS schedulers could nicely switch on-the-fly between cores with different instruction set capabilities, it's essentially not use-able.

moonchild 4y ago
> it's not clear how OS schedulers could nicely switch on-the-fly between cores with different instruction set capabilities It is a software problem, and it could have been solved with software. It was simply assumed a priori that it couldn't be solved, so no one bothered to try.
- wmf 4y ago
  Or they talked to Microsoft who said it would take years to add that feature.
  - undersuit 4y ago
    Or they talked with Microsoft who refused to add it to anything but Windows 11. Or maybe they can't handle it because of some difficiency in their Linux ports. The thing is it is possible and Intel knew for years that the E-cores wouldn't have AVX512.
  - moonchild 4y ago
    Let it take years, then. Leaving it disabled in the bios by default is one thing, and a rather reasonable one at that. Fusing it off is quite another.
- Twirrim 4y ago
  This isn't a new decision, it came out a few years ago that you'd end up with disparate instruction sets between the main and efficiency cores, and they got warned it would be a problem. Their disabling of the instructions to avoid it came about as a response. Both Microsoft and Linux devs warned them about the difficulties it'd present.