[PATCH v3 06/17] timer: Keep the pinned timers separate from the others

Anna-Maria Behnsen
2022-10-25T13:59:35Z

Seperate the storage space for pinned timers.

This is preparatory work for changing the NOHZ timer placement from a push
at enqueue time to a pull at expiry time model.

No functional change.

Originally-by: Richard Cochran (linutronix GmbH) <richardcochran@gmail.com>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
---
kernel/time/timer.c | 109 ++++++++++++++++++++++++++++++++------------
1 file changed, 81 insertions(+), 28 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index cb4194ecca60..b3eea90cb212 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -187,12 +187,18 @@ EXPORT_SYMBOL(jiffies_64);
#define WHEEL_SIZE (LVL_SIZE * LVL_DEPTH)

#ifdef CONFIG_NO_HZ_COMMON
-# define NR_BASES 2
-# define BASE_STD 0
-# define BASE_DEF 1
+/*
+ * If multiple bases need to be locked, use the base ordering for lock
+ * nesting, i.e. lowest number first.
+ */
+# define NR_BASES 3
+# define BASE_LOCAL 0
+# define BASE_GLOBAL 1
+# define BASE_DEF 2
#else
# define NR_BASES 1
-# define BASE_STD 0
+# define BASE_LOCAL 0
+# define BASE_GLOBAL 0
# define BASE_DEF 0
#endif

@@ -902,7 +908,10 @@ static int detach_if_pending(struct timer_list *timer, struct timer_base *base,

static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
{
- struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu);
+ int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
+ struct timer_base *base;
+
+ base = per_cpu_ptr(&timer_bases[index], cpu);

/*
* If the timer is deferrable and NO_HZ_COMMON is set then we need
@@ -915,7 +924,10 @@ static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)

static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
{
- struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
+ struct timer_base *base;
+
+ base = this_cpu_ptr(&timer_bases[index]);

/*
* If the timer is deferrable and NO_HZ_COMMON is set then we need
@@ -1700,9 +1712,10 @@ static unsigned long next_timer_interrupt(struct timer_base *base)
*/
u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
{
- struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ unsigned long nextevt, nextevt_local, nextevt_global;
+ struct timer_base *base_local, *base_global;
+ bool local_first, is_idle;
u64 expires = KTIME_MAX;
- unsigned long nextevt;

/*
* Pretend that there is no timer pending if the cpu is offline.
@@ -1711,38 +1724,69 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
if (cpu_is_offline(smp_processor_id()))
return expires;

- raw_spin_lock(&base->lock);
+ base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
+ base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);

- nextevt = next_timer_interrupt(base);
+ raw_spin_lock(&base_local->lock);
+ raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
+
+ nextevt_local = next_timer_interrupt(base_local);
+ nextevt_global = next_timer_interrupt(base_global);

/*
* We have a fresh next event. Check whether we can forward the
* base. We can only do that when @basej is past base->clk
* otherwise we might rewind base->clk.
*/
- if (time_after(basej, base->clk)) {
- if (time_after(nextevt, basej))
- base->clk = basej;
- else if (time_after(nextevt, base->clk))
- base->clk = nextevt;
+ if (time_after(basej, base_local->clk)) {
+ if (time_after(nextevt_local, basej))
+ base_local->clk = basej;
+ else if (time_after(nextevt_local, base_local->clk))
+ base_local->clk = nextevt_local;
+ }
+
+ if (time_after(basej, base_global->clk)) {
+ if (time_after(nextevt_global, basej))
+ base_global->clk = basej;
+ else if (time_after(nextevt_global, base_global->clk))
+ base_global->clk = nextevt_global;
}

/*
- * Base is idle if the next event is more than a tick away. Also
+ * Check whether the local event is expiring before or at the same
+ * time as the global event.
+ *
+ * Note, that nextevt_global and nextevt_local might be based on
+ * different base->clk values. So it's not guaranteed that
+ * comparing with empty bases results in a correct local_first.
+ */
+ if (base_local->timers_pending && base_global->timers_pending)
+ local_first = time_before_eq(nextevt_local, nextevt_global);
+ else
+ local_first = base_local->timers_pending;
+
+ nextevt = local_first ? nextevt_local : nextevt_global;
+
+ /*
+ * Bases are idle if the next event is more than a tick away. Also
* the tick is stopped so any added timer must forward the base clk
* itself to keep granularity small. This idle logic is only
- * maintained for the BASE_STD base, deferrable timers may still
- * see large granularity skew (by design).
+ * maintained for the BASE_LOCAL and BASE_GLOBAL base, deferrable
+ * timers may still see large granularity skew (by design).
*/
- base->is_idle = time_after(nextevt, basej + 1);
+ is_idle = time_after(nextevt, basej + 1);
+
+ /* We need to mark both bases in sync */
+ base_local->is_idle = base_global->is_idle = is_idle;

- if (base->timers_pending) {
+ if (base_local->timers_pending || base_global->timers_pending) {
/* If we missed a tick already, force 0 delta */
if (time_before_eq(nextevt, basej))
nextevt = basej;
expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
}
- raw_spin_unlock(&base->lock);
+ raw_spin_unlock(&base_global->lock);
+ raw_spin_unlock(&base_local->lock);

return cmp_next_hrtimer_event(basem, expires);
}
@@ -1754,7 +1798,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
*/
void timer_clear_idle(void)
{
- struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_LOCAL]);

/*
* We do this unlocked. The worst outcome is a remote enqueue sending
@@ -1763,6 +1807,9 @@ void timer_clear_idle(void)
* the lock in the exit from idle path.
*/
base->is_idle = false;
+
+ base = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
+ base->is_idle = false;
}
#endif

@@ -1808,11 +1855,13 @@ static inline void __run_timers(struct timer_base *base)
*/
static __latent_entropy void run_timer_softirq(struct softirq_action *h)
{
- struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_LOCAL]);

__run_timers(base);
- if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
+ if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
+ __run_timers(this_cpu_ptr(&timer_bases[BASE_GLOBAL]));
__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
+ }
}

/*
@@ -1820,17 +1869,21 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
*/
static void run_local_timers(void)
{
- struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+ struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_LOCAL]);

hrtimer_run_queues();
/* Raise the softirq only if required. */
if (time_before(jiffies, base->next_expiry)) {
if (!IS_ENABLED(CONFIG_NO_HZ_COMMON))
return;
- /* CPU is awake, so check the deferrable base. */
+ /* CPU is awake, so check for the global base. */
base++;
- if (time_before(jiffies, base->next_expiry))
- return;
+ if (time_before(jiffies, base->next_expiry)) {
+ /* CPU is awake, so check the deferrable base. */
+ base++;
+ if (time_before(jiffies, base->next_expiry))
+ return;
+ }
}
raise_softirq(TIMER_SOFTIRQ);
}
--
2.30.2