Thoughts on software-defined silicon [LWN.net]

Thoughts on software-defined silicon

Posted Feb 23, 2022 22:57 UTC (Wed) by Trelane (guest, #56877)
In reply to: Thoughts on software-defined silicon by atnot
Parent article: Thoughts on software-defined silicon

> Processors there are already highly segmented, with dozens of SKUs that only differ in what fuses are blown in them in the factory.

The reason for this is because defects happen (semiconductor chip joke for free, right there). If you have a problem in a redundant part of you chip, you can close it off and sell the rest of the perfectly good chip at a lower price point. Or lower the clockspeed, whatever.

Interestingly, this is the opposite: it had _better_ have passed qual, but now it is walled off until the customer pays up.

> can be a real benefit for enterprise customers, as they would presumably need to order and stock fewer CPU variants.

On inventory: presumably this will need to be locked to the exact processor. (Or how else do you prevent copying the cert and enabling the functionality on _another_ chip? Maybe phone home? Contact a flex_lm install on your network?) So now you have to track the certs for your chip in _addition_ to the chip itself! Alternately, maybe it stays once enabled sweet, now you have to track the _variants_ of the same chip.

I don't see the upside honestly.

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Thoughts on software-defined silicon

Posted Feb 23, 2022 23:52 UTC (Wed) by atnot (guest, #124910) [Link]

> The reason for this is because defects happen (semiconductor chip joke for free, right there). If you have a problem in a redundant part of you chip, you can close it off and sell the rest of the perfectly good chip at a lower price point. Or lower the clockspeed, whatever.

As I pointed out elsewhere, the degree to which this happens is greatly overstated by semiconductor companies. True, not every chip is going to reach the full clock speed and have all cores working. But for one, especially on mature nodes, the majority of them do and also that doesn't apply for many other lines they already segment along like maximum memory capacity, ECC, software features like Ryzen PRO/vPro etc. The far majority of chips are cut down because they wouldn't sell at a higher price, not because they are defective in any meaningful way. They do this because relatively speaking, the individual chips are dirt cheap (tens of dollars), all of the cost is in the NRE.

> So now you have to track the certs for your chip in _addition_ to the chip itself! Alternately, maybe it stays once enabled sweet, now you have to track the _variants_ of the same chip.

It is generally rare for a cpu to leave a system after it gets put in and tracking per-device licenses already needs to be done for all of the other hardware like switches, BMCs, etc. so it's not really a lot of extra effort for them.