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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.

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The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed (thehftguy.com)

submitted 10 months ago by [email protected] to c/[email protected]

28 comments fedilink hide all child comments

"The min_granularity setting was renamed to base_slice in this commit in v6 kernel.

The comment says it scales with CPU count and the comment is incorrect. I wonder whether kernel developers are aware of that mistake as they are rewriting the scheduler!

Official comments in the code says it’s scaling with log2(1+cores) but it doesn’t.
All the comments in the code are incorrect.
Official documentation and man pages are incorrect.
Every blog article, stack overflow answer and guide ever published about the scheduler is incorrect."

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[–] [email protected] 7 points 10 months ago (3 children)

How has no one noticed a server first kernel being limited to 8 cores?

[–] [email protected] 23 points 10 months ago (2 children)

Because it isn't. This impacts when the scheduler kicks in, not on how many cores stuff is running on. With fewer cores scheduler is faster triggered again, and and at 8 cores the adjustment for that stops. Which may be an intentional decision to avoid high latency issues.

[–] [email protected] 0 points 10 months ago (1 children)

@aard @Fizz
Wasn't the scheduler a one byte/bit at a time on/off scheme at some point?

[–] [email protected] 2 points 10 months ago

Yeah its mum used to say "you eat to fast eat one byte at a time"