Intel tells mobo makers to disable AVX-512 from Alder Lake CPUs via BIOS updates | Hacker News Reader

Intel tells mobo makers to disable AVX-512 from Alder Lake CPUs via BIOS updates

wccftech.com

27 pointsxmcqdpt210 comments

To clarify, the CPU wasn’t validated, tested, or binned with AVX-512 operation in mind. You also can’t just enable AVX-512 in the BIOS. You have to disable the efficiency cores first, resulting in a net slower CPU in multithreaded apps unless you have some very specific workload that uses AVX-512. There are also potential quirks with stability, thermals, and clock speed because AVX-512 normally alters clock speed, which presumably wasn’t tested or validated much if they never intended to ship it.

Realistically, I doubt there are many people out there who are interested in disabling some CPU cores to make a specific AVX-512 workload run faster on a consumer chip. It’s also not ideal to have a weird software support loophole where a specific CPU won’t have AVX-512 instructions except for maybe weird circumstances where someone enabled it.

I don't know, it seems like the sort of thing the build-your-own-PC crowd likes to experiment with. Overclocking also comes with all sorts of "potential quirks with stability, thermals, and clock speed", and is also not tested or validated, but tons of people do it anyway.

I imagine this could be useful for iterated crypto use cases, where you need to brute force hash(hash(hash(…))) as quickly as possible, you can’t parallelize by design, and some hardware failure is acceptable for extra speed.

Perhaps this is a way for Intel to either avoid their inventory being eaten up by miners solving these problems, or to upsell to other CPU lines?

The concerning part of this is that it sounds like they're only doing it because they accidentally gave a good feature to one of their cheaper parts, not for any legitimate technical reason.

You have to disable the efficiency cores to make it work, so it’s not exactly a net win unless you have some heavily AVX-512 workloads exclusively. The number of people who might benefit from this is extremely small.

I’m guessing it’s more likely that they didn’t validate the chips for AVX-512 operation when selecting the thermal and power limits, and they’d really rather not have them coming back at higher warranty rates.

> they’d really rather not have them coming back at higher warranty rates.

That would suggest that people are using them in enough quantities to warrent Intel "asking" for the functionality to be disabled.

> I’m guessing it’s more likely that they didn’t validate the chips for AVX-512 operation when selecting the thermal and power limits, and they’d really rather not have them coming back at higher warranty rates.

These are K parts. They're built for overclocking. People are going to take them outside of their thermal and power limits anyway.

Probably an issue with scheduling P/E cores when they don’t support exactly the same instruction set

As with all things, AVX512 involves a tradeoff: core frequency can decrease when it's in use; if properly utilized, it can realize significant performance gains, but if not, can result in a reduction in performance.

Don't be so quick to assume that a fence wasn't put up for a good reason.

But why not let the user make the choice? Why does Intel need to force it?

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