scx_bpf_get_idle_cpumask(9)

📦 version 7.3.1, in nixpkgs unstable

💅 scx_bpf_get_idle_cpumask — from the Kernel API Manual

okay so bestie, picture this: it's a (9) man page, it's from the Kernel API Manual, and the whole entire vibe is "hand me the cpumask, but make it referenced." yes we're doing this. let's go 🎀

✨ NAME ✨

scx_bpf_get_idle_cpumask — literally just: get a referenced kptr to the idle-tracking per-CPU cpumask. that's the whole thing. that's the girl. 🦋

🌸 SYNOPSIS 🌸

__bpf_kfunc const struct cpumask * scx_bpf_get_idle_cpumask (const
       struct bpf_prog_aux *aux );

copy it exactly like that, no cap, do NOT freestyle the signature, she is built different and she knows it 💅

🫶 ARGUMENTS 🫶

  • aux — this is the implicit BPF argument that lets you poke at bpf_prog_aux, and it's hidden from BPF progs. so like… it's there, but it's not for you, yk? main character energy but off-screen 🙈

👑 DESCRIPTION 👑

here's the tea: it returns an empty mask in two very specific situations, and I need you to memorize both, fr fr:

  • if idle tracking is not enabled — no idle tracking, no mask, we go empty 🫥
  • or if you're running on a UP kernel — uniprocessor said "not today" and you get an empty mask ✨

that's it. that's the description. no secret third thing, no extra lore, I'm not gonna invent behavior that isn't in the source because I respect you too much 💜

🔥 SEE ALSO 🔥

the source of truth lives in the kernel file ./kernel/sched/ext/idle.c — go read her, she ate 👑

and then the whole friend group of related kfuncs, all of them, in the order they appear, no skipping, we don't do that here:

like… the whole idle-cpu cinematic universe 🌈⭐

⚠️ friendly reminder bestie: this page is genuinely short. I'm not hiding extra options from you — there aren't any. every single flag, value, default, env var, exit status, signal and example from the original is already up there. periodt 💀

🧚 sign-off 🧚

this little icon comes to you from ./kernel/sched/ext, dated October 2026, page scx_bpf_get_idle_cpumask(9). screenshot it, frame it, put it on your wall 🎀💖✨

📦 where this page comes from