STRUCT TMIGR_HIERARCHY(9)

💖 struct tmigr_hierarchy(9) 💖

okay so bestie, welcome to the struct tmigr_hierarchy(9) page from the Kernel API Manual — yes it's a kernel struct, yes it's lowkey iconic, and yes I'm gonna walk you through it like we're annotating it in the group chat 🫶

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🎀 NAME 🎀

struct tmigr_hierarchy — it's a hierarchy that's associated to a given CPU capacity. that's the whole vibe ✨

Here's the tea though: homogeneous systems only get one hierarchy. heterogenous systems get one hierarchy per CPU capacity. so like, more capacity variety = more hierarchies, periodt 💅

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🌸 SYNOPSIS 🌸

struct tmigr_hierarchy {
    struct cpumask          *cpumask;
    struct tmigr_group      *root;
    unsigned long           capacity;
    struct list_head        node;
    struct list_head        level_list[];
};

look at her. so structured. so organized. main character struct fr fr 👑

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✨ Members ✨

so this is the part where we meet everybody in the struct, one by one, no skipping 🥰

• cpumask — the CPUs that belong to this hierarchy. it's a pointer to a struct cpumask, and it's literally the guest list for this hierarchy's party 💖
• root — the current root of the hierarchy. a struct tmigr_group pointer, and it's giving "the one at the top of the tree" energy 🌳👑
• capacity — the CPU capacity that's associated to this hierarchy, typed as unsigned long. this is the little label that tells you which capacity club this hierarchy belongs to 🎀
• node — a struct list_head that is this thing's node in the global hierarchy list. so she's linked up with all her sister hierarchies, iykyk 🔗
• level_list — per level lists of tmigr groups. note the [] — it's a flexible-ish trailing array of struct list_head, so there's one list per level, bestie 📚✨

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🦋 SEE ALSO 🦋

go read these next, they're all in the kernel file ./kernel/time/timer_migration.h and they're all part of the same friend group 💜

• struct tmigr_event(9)
• struct tmigr_group(9)
• struct tmigr_cpu(9)
• union tmigr_state(9)

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ngl this struct is small but she's doing a LOT of work. respect the capacity partitioning, okay? 🫶

and that's the page!! this one came from ./kernel/time and the date on it is October 2026, so like, mark your calendars bestie 😭💖 slay, go read your kernel source, and remember: every hierarchy deserves its own capacity. periodt 🌈⭐