STRUCT EM_PERF_DOMAIN(9)

okay so bestie, welcome to the struct em_perf_domain(9) page from the Kernel API Manual — no cap, this is the Performance domain struct and we're gonna cover every single member 💅✨

💖 NAME 💖

struct em_perf_domain — Performance domain. that's the name, and yes it's giving main-character kernel-struct energy 👑

✨ SYNOPSIS ✨

Here's the whole shape, literally, don't touch the code bestie:

struct em_perf_domain {
    struct em_perf_table *em_table;
    struct list_head node;
    int id;
    int nr_perf_states;
    int min_perf_state;
    int max_perf_state;
    unsigned long flags;
    unsigned long cpus[];
};

🌸 Members 🌸

Okay, member-by-member vibe check, bestie — every single one is here:

• em_table — Pointer to the runtime modifiable em_perf_table. literally a pointer, and it points at the runtime modifiable table, periodt 💅
• node — node in em_pd_list (in energy_model.c). iykyk 🎀
• id — a unique ID number for each performance domain. every PD gets its own lil ID 🦋
• nr_perf_states — Number of performance states. not me counting states 💀
• min_perf_state — Minimum allowed Performance State index. lowercase "minimum allowed", iconic boundary behavior ✨
• max_perf_state — Maximum allowed Performance State index. the other boundary, equally iconic ✨
• flags — See "em_perf_domain flags". yes bestie, go look at the flags 🌈
• cpus — Cpumask covering the CPUs of the domain. It's here for performance reasons to avoid potential cache misses during energy calculations in the scheduler and simplifies allocating/freeing that memory region. literally here for speed and memory-management convenience 🫶

🦋 Description 🦋

In case of CPU device, a "performance domain" represents a group of CPUs whose performance is scaled together — think squad of CPUs moving as one, but technical 💜

All CPUs of a performance domain must have the same micro-architecture. that's mandatory, no mixing vibes there.

Performance domains often have a 1-to-1 mapping with CPUFreq policies. yes bestie, often 1-to-1, not always, okay? 🙈

In case of other devices the cpus field is unused — so don't come for it, it's just sitting there unused in those cases 💀

🔥 SEE ALSO 🔥

Kernel file ./include/linux/energy_model.h — go read these next, bestie:

• struct em_perf_state(9)
• struct em_perf_table(9)
• em_pd_get_efficient_state(9)
• em_cpu_energy(9)
• em_pd_nr_perf_states(9)
• em_perf_state_from_pd(9)

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xoxo bestie, this struct em_perf_domain(9) page came from ./include/linux and it's dated October 2026 — mwah 💖🦋✨