How many in-order cores could one fit on a die? [LWN.net]

How many in-order cores could one fit on a die?

Posted Aug 11, 2023 9:52 UTC (Fri) by paulj (subscriber, #341)
In reply to: How many in-order cores could one fit on a die? by DemiMarie
Parent article: Another round of speculative-execution vulnerabilities

Several times more. Sun Niagara T1 had 8 cores X 4 threads = 64 threads, at a time when the complex OOO CPUs had 4 cores max with 2-way SMT (8 threads).

That machine got considerably more throughput on highly parallel web workloads as a result (as long as you didn't run a web app in a language that indiscriminately used floating-point, like PHP, cause they gave it one FPU to share between all cores!).

See link in another comment to a blog post with more details and references to a couple of really good papers - old, but still good reading.

to post comments

How many in-order cores could one fit on a die?

Posted Aug 11, 2023 11:19 UTC (Fri) by malmedal (subscriber, #56172) [Link] (3 responses)

> as long as you didn't run a web app in a language that indiscriminately used floating-point, like PHP

At one point I tried explaining to people, complete with benchmarks, why the Niagaras were not a good fit for a specific PHP application. It is quite difficult to convince people that the new expensive system they just bought will never work as well as the existing several years old servers it was supposed to replace.

Since the servers were bought and paid for I tried to find something useful for them to do, but did not really succeed.

How many in-order cores could one fit on a die?

Posted Aug 11, 2023 12:03 UTC (Fri) by paulj (subscriber, #341) [Link] (2 responses)

It was quite amazing that, in all the years it must have taken to get Niagara from concept through to actual servers, a CPU designed explicitly for loads like web serving, that no one really considered that a lot of web applications (esp then) are written in languages/frameworks that just use FP for all arithmetic.

How many in-order cores could one fit on a die?

Posted Aug 14, 2023 10:21 UTC (Mon) by epa (subscriber, #39769) [Link] (1 responses)

PHP and other scripting languages like Perl treat numbers as double-precision floating point but a lot of the time they are only smallish integers in practice. With a small amount of silicon you could give each core a 'fake FPU' that performs the necessary integer operations. If it turns out the inputs or the result aren't integer, it waits for the real FPU to become available.

How many in-order cores could one fit on a die?

Posted Aug 15, 2023 4:47 UTC (Tue) by donald.buczek (subscriber, #112892) [Link]

> PHP and other scripting languages like Perl treat numbers as double-precision floating point but a lot of the time they are only smallish integers in practice.

Not true for Perl, integers and doubles use native types [1].

[1]: https://github.com/Perl/perl5/blob/79c6bd015ed156a95e3480...