STRUCT HRTIMER_CPU_BASE(9)

🎀 struct hrtimer_cpu_base(9) 🎀

okay so bestie, welcome to the Kernel API Manual page for struct hrtimer_cpu_base — this is the per cpu clock bases, and it's honestly such a main character struct. it holds all the timer bookkeeping for one CPU, and every field is here so we're going through all of them, no skipping, periodt ✨

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💖 NAME 💖

struct hrtimer_cpu_base — the per cpu clock bases 🌸

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✨ SYNOPSIS ✨

struct hrtimer_cpu_base {
    raw_spinlock_t lock;
    unsigned int                    cpu;
    unsigned int                    active_bases;
    u32 clock_was_set_seq;
    bool hres_active;
    bool deferred_rearm;
    bool deferred_needs_update;
    bool hang_detected;
    bool softirq_activated;
    bool online;
  #ifdef CONFIG_HIGH_RES_TIMERS;
    unsigned int                    nr_events;
    unsigned short                  nr_retries;
    unsigned short                  nr_hangs;
    unsigned int                    max_hang_time;
  #endif;
  #ifdef CONFIG_PREEMPT_RT;
    spinlock_t softirq_expiry_lock;
    atomic_t timer_waiters;
  #endif;
    ktime_t expires_next;
    struct hrtimer                  *next_timer;
    ktime_t softirq_expires_next;
    struct hrtimer                  *softirq_next_timer;
    ktime_t deferred_expires_next;
    struct hrtimer_clock_base       clock_base[HRTIMER_MAX_CLOCK_BASES];
    call_single_data_t csd;
 };

quick vibe check on that: some of these fields only exist when CONFIG_HIGH_RES_TIMERS or CONFIG_PREEMPT_RT is on, so like… conditional queen behavior 💅

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🫶 Members (the good part, fr fr)

• lock — the lock protecting the base and the associated clock bases and timers. it's giving bodyguard energy 🔥
• cpu — the cpu number. literally just which CPU this whole thing belongs to.
• active_bases — a Bitfield to mark bases with active timers 👑
• clock_was_set_seq — Sequence counter of clock was set events. yes it counts them, someone has to 📊
• hres_active — State of high resolution mode. the high-res situation report ✨
• deferred_rearm — A deferred rearm is pending. it's on the to-do list bestie 💅
• deferred_needs_update — The deferred rearm must re-evaluate the first timer. like, it has to go back and re-check the first one 🫶
• hang_detected — The last hrtimer interrupt detected a hang. red flag, literally 😭
• softirq_activated — displays, if the softirq is raised - update of softirq related settings is not required then. so if this is up, no update needed, we can chill 💀
• online — CPU is online from an hrtimers point of view 🦋
• nr_events — Total number of hrtimer interrupt events
• nr_retries — Total number of hrtimer interrupt retries
• nr_hangs — Total number of hrtimer interrupt hangs
• max_hang_time — Maximum time spent in hrtimer_interrupt
• softirq_expiry_lock — Lock which is taken while softirq based hrtimer are expired
• timer_waiters — A hrtimer_cancel waiters for the timer callback to finish. they're waiting, be patient 🥺
• expires_next — Absolute time of the next event, is required for remote hrtimer enqueue; it is the total first expiry time (hard and soft hrtimer are taken into account). both flavors accounted for, no cap ⭐
• next_timer — Pointer to the first expiring timer
• softirq_expires_next — Time to check, if soft queues needs also to be expired
• softirq_next_timer — Pointer to the first expiring softirq based timer
• deferred_expires_next — Cached expires next value for deferred rearm 🎀
• clock_base — Array of clock bases for this cpu 🌈

side note: csd (a call_single_data_t) is in the struct up in the synopsis, but this page doesn't give it a member writeup — so i'm not out here making one up 🙈 the four nr_*/max_hang_time fields above are the CONFIG_HIGH_RES_TIMERS ones, and softirq_expiry_lock + timer_waiters are the CONFIG_PREEMPT_RT ones. iykyk 💜

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📝 Note 📝

⚠️ next_timer is just an optimization for __remove_hrtimer. Do not dereference the pointer because it is not reliable on cross cpu removals. seriously bestie, hands off the pointer on this one 💀

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/hrtimer_bases.h
• struct hrtimer_clock_base(9)

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okay that's the whole page, you ate that 🍓 this came to you from ./include/linux, dated October 2026, and it's the struct hrtimer_cpu_base(9) page — go forth and schedule responsibly, mwah 💖🧚