Thoughts on software-defined silicon [LWN.net]

Thoughts on software-defined silicon

Posted Feb 19, 2022 15:11 UTC (Sat) by jhoblitt (subscriber, #77733)
In reply to: Thoughts on software-defined silicon by khim
Parent article: Thoughts on software-defined silicon

It isn't just an issue of competition in the market. Fab capacity of each company and the overall market is a factor. Currently, the entire world is maxed out on wafer starts. So while it probably saves on masks, validation, etc. to cripple a perfectly functional 16core die to be sold as an 8core die, that means there is an 8core die area of silicon that is now lost. In a situation where every cpu produce can be sold, that lost real estate represents a potential 100% increase in gross margin.

to post comments

Thoughts on software-defined silicon

Posted Feb 19, 2022 15:19 UTC (Sat) by khim (subscriber, #9252) [Link] (2 responses)

If we have lived in a world where every CPU can be sold then we would have seen similar craziness to GPU market where prices are 2x-3x recommended price.

And GPU makers don't, actually, embrace that craziness, they fear it because they know what comes next: governments would say that cryptocurrency mining is a criminal activity, GPU sales would drop through the floor and they would be selling them at loss for some time.

Fab capacity is strained not because it's impossible to build mode fabs, but because it's impossible to do that profitably: build cycles are many years, investment are measured in billions and unused fabs are not aging well.

Thus no, your reasoning doesn't make sense long-term. And CPU/GPU manufacturing is long-term process, it takes many years to develop CPU from scratch and year or two just to do minor alterations.

Thoughts on software-defined silicon

Posted Feb 19, 2022 16:10 UTC (Sat) by jhoblitt (subscriber, #77733) [Link] (1 responses)

I was just quoted a 26+ week lead time on any zen3 epyc cpu with >= 32cores from a major manufacturer. I ended up accepting zen2 cores in order to cut the estimated lead time in half. However, the price will start to float at the market rate 90days from the date the quote was issued. I won't even know the final cost until I'm invoiced for the shipment. If this isn't a CPU shortage, I don't know what one would look like.

The GPU and CPU makers are all bidding on the same fab capacity. When AMD reserves wafers at TSMC, that's capacity that is denied to Apple/Nvidia/Intel/etc. and vice versa.

The ability to build new fabs is not unlimited. Bleeding edge fabs need equipment from ASML who reports that they and their supply chain are already maxed out. The world is essentially already building new fab capacity at the maximum rate they can get lithography equipment.

The rumors are that TSMC is booked out *years* in advance at the 5, 4, and 3nm nodes. Are you arguing that AMD is going to produce 128core zen4s and then cripple perfect dies down to 16c core parts instead of taping out multiple designs that use the exact same logical blocks, when all that lost real estate could have instead been used for GPUs or ~5-7 additional CPUs?

Thoughts on software-defined silicon

Posted Feb 19, 2022 17:12 UTC (Sat) by khim (subscriber, #9252) [Link]

> I was just quoted a 26+ week lead time on any zen3 epyc cpu with >= 32cores from a major manufacturer. I ended up accepting zen2 cores in order to cut the estimated lead time in half.

That's nice piece of data. Let's try to decipher it, shell we?

You asked for latest-and-greatest cores and got promise to receive them when they would be made (you may not know that, but half-year or more is not atypical if we are talking about manufacturing of complex 7nm chip: they require almost hundred masks and application of one mask takes full day or more, depending on how much load fab experiences right now). The exact same thing happened with surprisingly good R300 back when it was hot — yet somehow back then noone was bawling their eyes out and complained about shortage of fabs. Everyone accepted that it was simple management miscalculation.
When you asked for less “hot” chips made by the exact same manufacturer in the exact same lab by the exact same producer you got shorter times because, apparently because there are surplus of these in production.
Yet it's very easy to buy consumer-grade chips with Zen3 core. The full nomenclature from lowly Ryzen 5 5600X (which my friend bought in India two days ago) to Ryzen 9 5950X (which I bought at the same time). Prices are less than what recommended prices are. Many of these are artificially crippled.

Doesn't look like shortage of CPUs to me, sorry.

> If this isn't a CPU shortage, I don't know what one would look like.

Indeed, you don't know that. When you need to pay 10x or 100x price to receive 250nm chip (like some automotive chips are selling for right now) and situation stays that way for years — then you can say there are shortage of chips.

Till then it's normal reaction of market on changes in demand and supply for something that takes years to produce coupled with customers who, naïvely, expect to buy the same thing with lead times measured in weeks.

JIT-manufacturing, both good and bad sides of it.

> The rumors are that TSMC is booked out *years* in advance at the 5, 4, and 3nm nodes.

Why do you say these are rumors? That's the reality. Latest nodes are always booked years in advance. Because fabs are extremely expensive yet they can only ask for extra-premium prices for latest nodes for a few years… nobody builds spares. You don't even need rumors to confirm something that was always true.

> The GPU and CPU makers are all bidding on the same fab capacity.

Nope. That's not true because of, as you have said yourself: fab capacities are booked years in advance. Essentially they are booked when labs are built or maybe a bit later. If they are already booked then there are no competition between customers.

> When AMD reserves wafers at TSMC, that's capacity that is denied to Apple/Nvidia/Intel/etc. and vice versa.

No, they just build more fabs.

> Are you arguing that AMD is going to produce 128core zen4s and then cripple perfect dies down to 16c core parts instead of taping out multiple designs that use the exact same logical blocks, when all that lost real estate could have instead been used for GPUs or ~5-7 additional CPUs?

No, I'm saying that if you don't want shortages you don't disrupt markets by printing trillions of unbacked money and using all tricks you can imagine to avoid 40-50% inflation… mechanism where you have to calculate number of chips you need to order five years in advance but where buyers expect lead times measured in weeks works if you can predict number of buyers, but if you break that mechanism… it stops working. This is completely unrelated to selling crippling CPUs. Ryzen 5 5600X and Ryzen 9 5900 are still being produced and sold despite the fact that you can sell the exact same chips as Ryzen 7 5800X and Ryzen 9 5990X.

Turning 128 core chip into 16 core chip wouldn't make any sense because AMD embraces chiplets architecture thus you can just use more or less chiplets. But if you want to shave off 2 cores or 4 cores... AMD does that and is happy to sell these at discount prices.