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Subject[patch V2 04/10] timer: Keep the pinned timers separate from the others
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.

Signed-off-by: Richard Cochran <rcochran@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
kernel/time/timer.c | 98 +++++++++++++++++++++++++++++++++++++---------------
1 file changed, 70 insertions(+), 28 deletions(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -185,12 +185,14 @@ 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
+# 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

@@ -218,16 +220,18 @@ void timers_update_migration(bool update
unsigned int cpu;

/* Avoid the loop, if nothing to update */
- if (this_cpu_read(timer_bases[BASE_STD].migration_enabled) == on)
+ if (this_cpu_read(timer_bases[BASE_GLOBAL].migration_enabled) == on)
return;

for_each_possible_cpu(cpu) {
- per_cpu(timer_bases[BASE_STD].migration_enabled, cpu) = on;
+ per_cpu(timer_bases[BASE_LOCAL].migration_enabled, cpu) = on;
+ per_cpu(timer_bases[BASE_GLOBAL].migration_enabled, cpu) = on;
per_cpu(timer_bases[BASE_DEF].migration_enabled, cpu) = on;
per_cpu(hrtimer_bases.migration_enabled, cpu) = on;
if (!update_nohz)
continue;
- per_cpu(timer_bases[BASE_STD].nohz_active, cpu) = true;
+ per_cpu(timer_bases[BASE_LOCAL].nohz_active, cpu) = true;
+ per_cpu(timer_bases[BASE_GLOBAL].nohz_active, cpu) = true;
per_cpu(timer_bases[BASE_DEF].nohz_active, cpu) = true;
per_cpu(hrtimer_bases.nohz_active, cpu) = true;
}
@@ -810,7 +814,10 @@ static int detach_if_pending(struct time

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 nohz is active then we need to use
@@ -824,7 +831,10 @@ static inline struct timer_base *get_tim

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 nohz is active then we need to use
@@ -1468,10 +1478,10 @@ static u64 cmp_next_hrtimer_event(u64 ba
*/
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;
+ bool local_empty, global_empty, local_first, is_idle;
+ struct timer_base *base_local, *base_global;
u64 expires = KTIME_MAX;
- unsigned long nextevt;
- bool is_empty;

/*
* Pretend that there is no timer pending if the cpu is offline.
@@ -1480,26 +1490,49 @@ u64 get_next_timer_interrupt(unsigned lo
if (cpu_is_offline(smp_processor_id()))
return expires;

- spin_lock(&base->lock);
- is_empty = __next_timer_interrupt(base);
- nextevt = base->next_expiry;
+ base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
+ base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
+
+ spin_lock(&base_global->lock);
+ spin_lock_nested(&base_local->lock, SINGLE_DEPTH_NESTING);
+
+ local_empty = __next_timer_interrupt(base_local);
+ nextevt_local = base_local->next_expiry;
+
+ global_empty = __next_timer_interrupt(base_global);
+ nextevt_global = base_global->next_expiry;
+
/*
* 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. */
- base->is_idle = time_after(nextevt, basej + 1);
- spin_unlock(&base->lock);
+ local_first = time_before_eq(nextevt_local, nextevt_global);
+ nextevt = local_first ? nextevt_local : nextevt_global;
+ 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 (!is_empty) {
+ spin_unlock(&base_local->lock);
+ spin_unlock(&base_global->lock);
+
+ if (!local_empty || !global_empty) {
/* If we missed a tick already, force 0 delta */
if (time_before_eq(nextevt, basej))
nextevt = basej;
@@ -1516,7 +1549,7 @@ u64 get_next_timer_interrupt(unsigned lo
*/
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
@@ -1525,6 +1558,9 @@ 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;
}

static int collect_expired_timers(struct timer_base *base,
@@ -1614,11 +1650,17 @@ static inline void __run_timers(struct t
*/
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) && base->nohz_active)
- __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
+ if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
+ base = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
+ __run_timers(base);
+
+ base = this_cpu_ptr(&timer_bases[BASE_DEF]);
+ if (base->nohz_active)
+ __run_timers(base);
+ }
}

/*
@@ -1626,7 +1668,7 @@ static __latent_entropy void run_timer_s
*/
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. */

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