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hrtimer: Provide a static branch based hrtimer_hres_enabled()

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The scheduler evaluates this via hrtimer_is_hres_active() every time it has
to update HRTICK. This needs to follow three pointers, which is expensive.

Provide a static branch based mechanism to avoid that.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.136503358@kernel.org
This commit is contained in:
Thomas Gleixner
2026-02-24 17:35:42 +01:00
committed by Peter Zijlstra
parent d19ff16c11
commit 0a93d30861
2 changed files with 34 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
include/linux/hrtimer.h
View File

@@ -153,17 +153,22 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
}
#ifdef CONFIG_HIGH_RES_TIMERS
extern unsigned int hrtimer_resolution;
struct clock_event_device;
extern void hrtimer_interrupt(struct clock_event_device *dev);
extern unsigned int hrtimer_resolution;
extern struct static_key_false hrtimer_highres_enabled_key;
#else
static inline bool hrtimer_highres_enabled(void)
{
return static_branch_likely(&hrtimer_highres_enabled_key);
}
#else /* CONFIG_HIGH_RES_TIMERS */
#define hrtimer_resolution (unsigned int)LOW_RES_NSEC
#endif
static inline bool hrtimer_highres_enabled(void) { return false; }
#endif /* !CONFIG_HIGH_RES_TIMERS */
static inline ktime_t
__hrtimer_expires_remaining_adjusted(const struct hrtimer *timer, ktime_t now)

28
kernel/time/hrtimer.c
View File

@@ -126,6 +126,25 @@ static inline bool hrtimer_base_is_online(struct hrtimer_cpu_base *base)
return likely(base->online);
}
#ifdef CONFIG_HIGH_RES_TIMERS
DEFINE_STATIC_KEY_FALSE(hrtimer_highres_enabled_key);
static void hrtimer_hres_workfn(struct work_struct *work)
{
static_branch_enable(&hrtimer_highres_enabled_key);
}
static DECLARE_WORK(hrtimer_hres_work, hrtimer_hres_workfn);
static inline void hrtimer_schedule_hres_work(void)
{
if (!hrtimer_highres_enabled())
schedule_work(&hrtimer_hres_work);
}
#else
static inline void hrtimer_schedule_hres_work(void) { }
#endif
/*
* Functions and macros which are different for UP/SMP systems are kept in a
* single place
@@ -649,7 +668,9 @@ static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
}
/*
* Is the high resolution mode active ?
* Is the high resolution mode active in the CPU base. This cannot use the
* static key as the CPUs are switched to high resolution mode
* asynchronously.
*/
static inline int hrtimer_hres_active(struct hrtimer_cpu_base *cpu_base)
{
@@ -750,6 +771,7 @@ static void hrtimer_switch_to_hres(void)
tick_setup_sched_timer(true);
/* "Retrigger" the interrupt to get things going */
retrigger_next_event(NULL);
hrtimer_schedule_hres_work();
}
#else
@@ -947,11 +969,10 @@ static bool update_needs_ipi(struct hrtimer_cpu_base *cpu_base,
*/
void clock_was_set(unsigned int bases)
{
struct hrtimer_cpu_base *cpu_base = raw_cpu_ptr(&hrtimer_bases);
cpumask_var_t mask;
int cpu;
if (!hrtimer_hres_active(cpu_base) && !tick_nohz_is_active())
if (!hrtimer_highres_enabled() && !tick_nohz_is_active())
goto out_timerfd;
if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
@@ -962,6 +983,7 @@ void clock_was_set(unsigned int bases)
/* Avoid interrupting CPUs if possible */
cpus_read_lock();
for_each_online_cpu(cpu) {
struct hrtimer_cpu_base *cpu_base;
unsigned long flags;
cpu_base = &per_cpu(hrtimer_bases, cpu);