STRUCT EM_PERF_STATE(9)

💅 struct em_perf_state(9)

okay so bestie, welcome to struct em_perf_state(9) — the Kernel API Manual page that's genuinely about the performance state of a performance domain. yes that's the NAME section, and yes it ate. this is a struct, it lives in the kernel, and it's lowkey the main character of energy-aware scheduling. periodt. ✨

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🌈 SYNOPSIS 🌈

here's the whole vibe, literally character for character, don't touch:

struct em_perf_state {
    unsigned long performance;
    unsigned long frequency;
    unsigned long power;
    unsigned long cost;
    unsigned long flags;
 };

five unsigned long fields, all iconic, no notes. 🫶

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🎀 MEMBERS 🎀

• performance — the CPU performance (aka capacity) at a given frequency. it's giving "how much can you actually do at this clock speed" energy. 💪
• frequency — the frequency in KHz, kept in KHz for consistency with CPUFreq. yes, KHz, not MHz, not GHz, bestie — consistency is the moment here. ⭐
• power — the power consumed at this level (by 1 CPU or by a registered device). and ngl, it can be a total power: static and dynamic. both. together. 💀
• cost — the cost coefficient associated with this level, used during energy calculation. it's equal to:

10 * power * max_frequency / frequency

that's the whole formula, no cap. use it exactly. 🧮✨

• flags — see the "em_perf_state flags" description below. that's literally what it says, i'm just the messenger. 🙈

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🦋 SEE ALSO 🦋

• Kernel file ./include/linux/energy_model.h
• struct em_perf_table(9)
• struct em_perf_domain(9)
• em_pd_get_efficient_state(9)
• em_cpu_energy(9)
• em_pd_nr_perf_states(9)
• em_perf_state_from_pd(9)

go read those too, they're all in the same friend group, iykyk. 💜

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and that's the page, bestie! 🎀 this one's from ./include/linux, dated October 2026, and it's literally titled struct em_perf_state(9) — slay, go touch some energy model code, you got this 🌸💖