[tyfighter]

This is something I heard through the grape vine years ago, but when you're a very large corporation negotiating CPU purchasing contracts in quantities of millions, you can get customizations that aren't possible outside of gigantic data centers. Things like enabling custom microcode (and development support) for adding new instructions for the benefit of your custom JIT-ed server infrastructure. The corporate entity here is likely a hyperscaler that everyone knows.

[jeffbee]

Some of the public x86 ISA extensions were things that hyperscalers specifically requested.

[clausecker]

Such as?

[kijiki]

Most of the Intel cache partitioning things were driven primarily by Google. The holy grail was to colocate latency-sensitive tasks with bulk background tasks to increase cluster utilization.

[jeffbee]

I guess technically CAT and RDT are not ISA extensions because they are managed by MSRs. I was thinking of aspects of BMI, but I am sure that large-scale buyers had input into things like vector extensions, PMU features, and the things you mentioned as well.

[dboreham]

Historically the large buyer that could do this was NSA. Men in black would show up and tell you to add a bit population count instruction to your CPU..

[jeffbee]

I think it's doubtful that around the time that POPCNT was added to CPUs the NSA was all that influential. Their big scary data center, which is actually tiny, wasn't built until 2014, while players like Google and Meta had much larger data centers years earlier and were undoubtedly larger buyers of AMD Barcelona / Intel Westmere where POPCNT first emerged.

[aleph_minus_one]

Here is an article about the popcnt instruction:

https://vaibhavsagar.com/blog/2019/09/08/popcount/

The author of the article believes that while popcnt was indeed used for cryptographical analysis in the 60s, but the fact that popcnt disappeared from instruction sets is seen as evidence that this usage became a lot less important over time. So the author considers the reason for the reappearance of popcnt that there simply exist lots of other useful applications of popcnt that become evident over these decades.

A German article about the same topic:

https://nickyreinert.medium.com/ne-49-popcount-ea62aa304f88

[dboreham]

Oh, when I saw this happen first-hand, it was probably 1986.

Note that the first "data center" I know of was built at Bletchley Park in the 1940s.

[Maxious]

eg. "custom Intel Xeon 6 processors, available only on AWS." https://aws.amazon.com/blogs/aws/best-performance-and-fastes...

[renewiltord]

Oracle Cloud used to boast this as something they had. Tuned for OracleDB with more cache, different core count.

And every homelabber has had one of the 7B13 or 9654-variant processors