SCHED_ULE(4)

📦 version 12.2, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

💖 SCHED_ULE — the ULE scheduler, bestie edition 💖

ok so you're in the Kernel Interfaces Manual and we're talking about SCHED_ULE(4) — the scheduler that runs the whole show. sit down, hydrate, let's go 🫶

✨ NAME ✨

sched_ule — the ULE scheduler. that's it, that's the name, and it's iconic 💅

✨ SYNOPSIS ✨

options SCHED_ULE

literally one line. put it in your kernel config and you're done, no cap ✨

✨ DESCRIPTION ✨

okay so the sched_ule scheduler is giving advanced scheduler features that sched_4bsd(4) — the traditional system scheduler — simply does not have. it's not a competition but… it kind of is 😭 these features are all about SMP and interactivity, and they include:

  • Thread CPU affinity. 🧵
  • CPU topology awareness, including for hyper-threading. yes it knows your cores are siblings, it's not weird about it 🦋
  • Per-CPU run queues. everybody gets their own line, no pushing 🌸
  • Interactivity heuristics that detect interactive applications and schedule them preferentially under high load. the scheduler is basically a bouncer who recognizes the VIPs 👑

🎀 the sysctls that matter 🎀

these are the sysctls relevant to how sched_ule operates. learn them, love them, they're your besties now:

  • kern.sched.name — this one is read-only and it reports the name of the active scheduler. it just tells you who's on aux, it does not take requests 🙈
  • kern.sched.quantum — this one is read-write and it reports or sets the length of the quantum (in micro-seconds) granted to a thread. so you can peek, or you can change it. main character behaviour fr fr ⭐

✨ SEE ALSO ✨

go read them, they're part of the lore 📚

✨ HISTORY ✨

the sched_ule scheduler first appeared in FreeBSD 5.1. vintage but make it fast 💀✨

✨ AUTHORS ✨

Jeff Roberson <jeff@FreeBSD.org> — thank you for your service king 🫶👑

ok that's the whole page bestie, you're officially educated. go schedule something 💖

Debian — August 10, 2012 — SCHED_ULE(4) 🎀 and that's the vibe check, we're done here, periodt 💅🌈

📦 where this page comes from