cmask_from_cpumask(9)

💅 cmask_from_cpumask — the Kernel API Manual page, bestie edition 🎀

okay so this is cmask_from_cpumask(9) from the Kernel API Manual, and honestly? she's a tiny little translator and she slays at her one job. let's get into it ✨

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🌸 NAME 🌸

cmask_from_cpumask — translate a kernel cpumask to a cid-space cmask, no cap 🦋

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✨ SYNOPSIS ✨

void cmask_from_cpumask (struct scx_cmask __arena *m , const struct
cpumask *cpumask );

look at her. two args, no return, zero drama. iconic. 👑

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🎀 ARGUMENTS 🎀

• m — the cmask to fill, bestie. it gets zeroed first, and then only bits within [m->base, m->base + m->nr_cids) get updated. so if a cpu maps to a cid outside that range? it's getting ignored, sorry not sorry 💅
• cpumask — the kernel cpumask to translate. that's it, that's the whole vibe 🫶

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💖 DESCRIPTION 💖

so for each cpu in cpumask, it sets that cpu's cid in m. literally that's the whole thing. simple, clean, ate. 🔥

⚠️ but the tea is: the caller must ensure cpumask stays stable across the call — like, for example, holding an RCU read lock for task->cpus_ptr. do not let that thing shift under you mid-call, i am begging 😭

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🌈 SEE ALSO 🌈

• Kernel file ./tools/sched_ext/include/scx/cid.bpf.h
• __cmask_init(9)
• cmask_init(9)
• cmask_reframe(9)
• cmask_next_set(9)

go read them, they're the friend group, you can't just know one of them 💜

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kay that's the page!! source is ./tools/sched_ext/include/scx and this was dated October 2026 — mwah, bye bestie, go translate some cpumasks 💅🧚‍♀️⭐