scx_bpf_pick_idle_cpu_node(9)

💅 scx_bpf_pick_idle_cpu_node(9) — like, the kernel API manual bestie 🎀

okay so real talk, this is a page straight out of the Kernel API Manual and it's all about scx_bpf_pick_idle_cpu_node — a kfunc that goes and finds you a sleepy little cpu and claims it for you. no cap. ✨

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🌸 NAME 🌸

scx_bpf_pick_idle_cpu_node — pick and claim an idle cpu from @node fr fr 💖

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🦋 SYNOPSIS 🦋

__bpf_kfunc s32 scx_bpf_pick_idle_cpu_node (const struct cpumask
       *cpus_allowed , s32 node , u64 flags , const struct bpf_prog_aux *aux );

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✨ ARGUMENTS ✨

• cpus_allowed — the allowed cpumask, aka the guest list of cpus you're allowed to look at 💅
• node — the target NUMA node, like which neighborhood you're shopping in 🏘️
• flags — your SCX_PICK_IDLE_* flags, the little toggles that change the vibe check
• aux — an implicit BPF argument so you can access bpf_prog_aux, hidden from BPF progs 🙈 (not me, not you, it's just not for us)

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👑 DESCRIPTION 👑

Pick and claim an idle cpu in cpus_allowed from the NUMA node node. that's it, that's the whole thing 💖

Returns the picked idle cpu number on success, or -EBUSY if no matching cpu was found. 😭 so if it comes back with -EBUSY it's literally telling you "ma'am, there is nothing here".

The search starts from node and proceeds to other online NUMA nodes in order of increasing distance (unless SCX_PICK_IDLE_IN_NODE is specified, in which case the search is limited to the target node). so it'll wander further out, closest spots first, unless you pin it down with SCX_PICK_IDLE_IN_NODE — then it stays exactly where you told it to. 🎀

⚠️ Always returns an error if ops.update_idle is implemented and SCX_OPS_KEEP_BUILTIN_IDLE is not set, or if SCX_OPS_BUILTIN_IDLE_PER_NODE is not set. like, it's not being difficult, those are just the rules bestie 💀

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🌈 SEE ALSO 🌈

• Kernel file ./kernel/sched/ext/idle.c — the source, the mothership 🧚
• scx_bpf_cpu_node(9)
• scx_bpf_select_cpu_dfl(9)
• __scx_bpf_select_cpu_and(9)
• scx_bpf_get_idle_cpumask_node(9)
• scx_bpf_get_idle_cpumask(9)
• scx_bpf_get_idle_smtmask_node(9)
• scx_bpf_get_idle_smtmask(9)
• scx_bpf_put_idle_cpumask(9)
• scx_bpf_test_and_clear_cpu_idle(9)
• scx_bpf_pick_idle_cpu(9)
• scx_bpf_pick_any_cpu_node(9)
• scx_bpf_pick_any_cpu(9)

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that's the whole page, and honestly? she ate. 💅✨ this one lives over at ./kernel/sched/ext, dated October 2026, and the title card reads scx_bpf_pick_idle_cpu_node(9) — slay, go pick yourself an idle cpu, you got this 🫶💖🔥