scx_bpf_cpu_to_cid(9)

💅 scx_bpf_cpu_to_cid(9) — like, the Kernel API Manual, bestie ✨

okay so real talk, this page lives in the scx_bpf_cpu_to_cid(9) section of the kernel API manual and it's genuinely one of the shorter ones — a little snack, a lil palate cleanser 🍓

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✨ NAME ✨

scx_bpf_cpu_to_cid — returns the cid for @cpu 🎀

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🦋 SYNOPSIS 🦋

__bpf_kfunc s32 scx_bpf_cpu_to_cid (s32 cpu , const struct bpf_prog_aux
*aux );

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🌸 ARGUMENTS 🌸

• cpu — the cpu you're trying to look up, that's the whole vibe 💅
• aux — ngl this one is the implicit BPF argument, it's what gives you access to bpf_prog_aux, and it's literally hidden from BPF progs 🙈 so don't go looking for it, it's giving backstage pass

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🔥 DESCRIPTION 🔥

So you call this and it returns the cid for cpu. That's it, that's the function, main character energy fr fr 👑

But bestie, heads up: if cpu is invalid it triggers scx_error and returns -EINVAL 💀 so like, vibe check your cpu first, okay?

The iconic part? The cid<->cpu mapping is static for the lifetime of the loaded scheduler — so the BPF side can totally cache the result and skip repeated kfunc invocations. not me saving you a syscall 😌✨

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🌈 SEE ALSO 🌈

Kernel file ./kernel/sched/ext/cid.c plus the whole friend group:

• scx_cid_publish_tables(9)
• scx_cid_retire_tables(9)
• scx_cid_init(9)
• scx_cmask_clear(9)
• scx_cmask_fill(9)
• scx_bpf_cid_override(9)
• scx_bpf_cid_to_cpu(9)
• scx_cmask_subset(9)
• scx_cmask_empty(9)
• scx_bpf_cid_topo(9)
• scx_cmask_ref_init(9)
• scx_cmask_ref_init_kern(9)
• scx_cmask_ref_shard(9)
• scx_cmask_ref_or(9)
• scx_cmask_ref_copy(9)
• scx_cmask_ref_from_cpumask(9)

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🫶 and that's the whole page, periodt. this lil cutie came out of ./kernel/sched/ext and it's stamped October 2026 — so go forth, cache your cids, and slay 💖🎀⭐