Technology

58303 readers

12 users here now

This is a most excellent place for technology news and articles.

Our Rules

Follow the lemmy.world rules.
Only tech related content.
Be excellent to each another!
Mod approved content bots can post up to 10 articles per day.
Threads asking for personal tech support may be deleted.
Politics threads may be removed.
No memes allowed as posts, OK to post as comments.
Only approved bots from the list below, to ask if your bot can be added please contact us.
Check for duplicates before posting, duplicates may be removed

Approved Bots

founded 1 year ago

MODERATORS

[email protected]

335

Yes, you can have too many CPU cores - Ampere's 192-core chips break ARM64 Linux kernel in two-socket systems, company requests higher core count support (www.tomshardware.com)

submitted 1 year ago by [email protected] to c/[email protected]

39 comments fedilink hide all child comments

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 22 points 1 year ago

Well looking at the patch

+config NR_CPUS_RANGE_END
+	int
+	default 8192 if  SMP &amp;&amp; CPUMASK_OFFSTACK
+	default  512 if  SMP &amp;&amp; !CPUMASK_OFFSTACK
+	default    1 if !SMP
+

It looks like it's doing and end range of 8192 but with the off stack flag set. And it seems that…

+	  This is purely to save memory: each supported CPU adds about 8KB
+	  to the kernel image.

Which looks like they're trying to save memory to avoid TLB stalling on the CPU's bitmap. I think if the chip maker is indicating that slab allocation is fine for more at the moment (which the patch looks to be coming from Christoph Lameter, who works at Ampere), it's best to assume they've tested it on their end. Or at least I would think so. If they felt that more on the stack was a fine option, I would think that, that's exactly what they would pitch to the KML. Them saying there's a need for offstack past 512, I'm guessing there's a reason and the one I can think of is TLB stalls.