[patch 10/23] hrtimers: clean up locking

From: Thomas Gleixner
Date: Fri Sep 29 2006 - 20:10:55 EST

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

improve kernel/hrtimers.c locking: use a per-CPU base with a lock to
control locking of all clocks belonging to a CPU. This simplifies
code that needs to lock all clocks at once. This makes life easier
for high-res timers and dyntick. No functional change should happen
due to this.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
--
include/linux/hrtimer.h | 37 ++++++---
kernel/hrtimer.c | 181 +++++++++++++++++++++++++-----------------------
2 files changed, 121 insertions(+), 97 deletions(-)

Index: linux-2.6.18-mm2/include/linux/hrtimer.h
===================================================================
--- linux-2.6.18-mm2.orig/include/linux/hrtimer.h 2006-09-30 01:41:15.000000000 +0200
+++ linux-2.6.18-mm2/include/linux/hrtimer.h 2006-09-30 01:41:17.000000000 +0200
@@ -36,7 +36,7 @@ enum hrtimer_restart {

#define HRTIMER_INACTIVE ((void *)1UL)

-struct hrtimer_base;
+struct hrtimer_clock_base;

/**
* struct hrtimer - the basic hrtimer structure
@@ -50,10 +50,10 @@ struct hrtimer_base;
* The hrtimer structure must be initialized by init_hrtimer_#CLOCKTYPE()
*/
struct hrtimer {
- struct rb_node node;
- ktime_t expires;
- int (*function)(struct hrtimer *);
- struct hrtimer_base *base;
+ struct rb_node node;
+ ktime_t expires;
+ int (*function)(struct hrtimer *);
+ struct hrtimer_clock_base *base;
};

/**
@@ -68,31 +68,44 @@ struct hrtimer_sleeper {
struct task_struct *task;
};

+struct hrtimer_cpu_base;
+
/**
* struct hrtimer_base - the timer base for a specific clock
* @index: clock type index for per_cpu support when moving a timer
* to a base on another cpu.
- * @lock: lock protecting the base and associated timers
* @active: red black tree root node for the active timers
* @first: pointer to the timer node which expires first
* @resolution: the resolution of the clock, in nanoseconds
* @get_time: function to retrieve the current time of the clock
* @get_softirq_time: function to retrieve the current time from the softirq
- * @curr_timer: the timer which is executing a callback right now
* @softirq_time: the time when running the hrtimer queue in the softirq
- * @lock_key: the lock_class_key for use with lockdep
*/
-struct hrtimer_base {
+struct hrtimer_clock_base {
+ struct hrtimer_cpu_base *cpu_base;
clockid_t index;
- spinlock_t lock;
struct rb_root active;
struct rb_node *first;
ktime_t resolution;
ktime_t (*get_time)(void);
ktime_t (*get_softirq_time)(void);
- struct hrtimer *curr_timer;
ktime_t softirq_time;
- struct lock_class_key lock_key;
+};
+
+#define HRTIMER_MAX_CLOCK_BASES 2
+
+/*
+ * struct hrtimer_cpu_base - the per cpu clock bases
+ * @lock: lock protecting the base and associated clock bases and timers
+ * @lock_key: the lock_class_key for use with lockdep
+ * @clock_base: array of clock bases for this cpu
+ * @curr_timer: the timer which is executing a callback right now
+ */
+struct hrtimer_cpu_base {
+ spinlock_t lock;
+ struct lock_class_key lock_key;
+ struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
+ struct hrtimer *curr_timer;
};

/*
Index: linux-2.6.18-mm2/kernel/hrtimer.c
===================================================================
--- linux-2.6.18-mm2.orig/kernel/hrtimer.c 2006-09-30 01:41:15.000000000 +0200
+++ linux-2.6.18-mm2/kernel/hrtimer.c 2006-09-30 01:41:17.000000000 +0200
@@ -1,8 +1,8 @@
/*
* linux/kernel/hrtimer.c
*
- * Copyright(C) 2005, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- * Copyright(C) 2005, Red Hat, Inc., Ingo Molnar
+ * Copyright(C) 2005-2006, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
+ * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
*
* High-resolution kernel timers
*
@@ -79,21 +79,22 @@ EXPORT_SYMBOL_GPL(ktime_get_real);
* This ensures that we capture erroneous accesses to these clock ids
* rather than moving them into the range of valid clock id's.
*/
-
-#define MAX_HRTIMER_BASES 2
-
-static DEFINE_PER_CPU(struct hrtimer_base, hrtimer_bases[MAX_HRTIMER_BASES]) =
+static DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
{
+
+ .clock_base =
{
- .index = CLOCK_REALTIME,
- .get_time = &ktime_get_real,
- .resolution = KTIME_REALTIME_RES,
- },
- {
- .index = CLOCK_MONOTONIC,
- .get_time = &ktime_get,
- .resolution = KTIME_MONOTONIC_RES,
- },
+ {
+ .index = CLOCK_REALTIME,
+ .get_time = &ktime_get_real,
+ .resolution = KTIME_REALTIME_RES,
+ },
+ {
+ .index = CLOCK_MONOTONIC,
+ .get_time = &ktime_get,
+ .resolution = KTIME_MONOTONIC_RES,
+ },
+ }
};

/**
@@ -125,7 +126,7 @@ EXPORT_SYMBOL_GPL(ktime_get_ts);
* Get the coarse grained time at the softirq based on xtime and
* wall_to_monotonic.
*/
-static void hrtimer_get_softirq_time(struct hrtimer_base *base)
+static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
{
ktime_t xtim, tomono;
unsigned long seq;
@@ -137,8 +138,9 @@ static void hrtimer_get_softirq_time(str

} while (read_seqretry(&xtime_lock, seq));

- base[CLOCK_REALTIME].softirq_time = xtim;
- base[CLOCK_MONOTONIC].softirq_time = ktime_add(xtim, tomono);
+ base->clock_base[CLOCK_REALTIME].softirq_time = xtim;
+ base->clock_base[CLOCK_MONOTONIC].softirq_time =
+ ktime_add(xtim, tomono);
}

/*
@@ -161,19 +163,20 @@ static void hrtimer_get_softirq_time(str
* possible to set timer->base = NULL and drop the lock: the timer remains
* locked.
*/
-static struct hrtimer_base *lock_hrtimer_base(const struct hrtimer *timer,
- unsigned long *flags)
+static
+struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
+ unsigned long *flags)
{
- struct hrtimer_base *base;
+ struct hrtimer_clock_base *base;

for (;;) {
base = timer->base;
if (likely(base != NULL)) {
- spin_lock_irqsave(&base->lock, *flags);
+ spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
return base;
/* The timer has migrated to another CPU: */
- spin_unlock_irqrestore(&base->lock, *flags);
+ spin_unlock_irqrestore(&base->cpu_base->lock, *flags);
}
cpu_relax();
}
@@ -182,12 +185,14 @@ static struct hrtimer_base *lock_hrtimer
/*
* Switch the timer base to the current CPU when possible.
*/
-static inline struct hrtimer_base *
-switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_base *base)
+static inline struct hrtimer_clock_base *
+switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base)
{
- struct hrtimer_base *new_base;
+ struct hrtimer_clock_base *new_base;
+ struct hrtimer_cpu_base *new_cpu_base;

- new_base = &__get_cpu_var(hrtimer_bases)[base->index];
+ new_cpu_base = &__get_cpu_var(hrtimer_bases);
+ new_base = &new_cpu_base->clock_base[base->index];

if (base != new_base) {
/*
@@ -199,13 +204,13 @@ switch_hrtimer_base(struct hrtimer *time
* completed. There is no conflict as we hold the lock until
* the timer is enqueued.
*/
- if (unlikely(base->curr_timer == timer))
+ if (unlikely(base->cpu_base->curr_timer == timer))
return base;

/* See the comment in lock_timer_base() */
timer->base = NULL;
- spin_unlock(&base->lock);
- spin_lock(&new_base->lock);
+ spin_unlock(&base->cpu_base->lock);
+ spin_lock(&new_base->cpu_base->lock);
timer->base = new_base;
}
return new_base;
@@ -215,12 +220,12 @@ switch_hrtimer_base(struct hrtimer *time

#define set_curr_timer(b, t) do { } while (0)

-static inline struct hrtimer_base *
+static inline struct hrtimer_clock_base *
lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
{
- struct hrtimer_base *base = timer->base;
+ struct hrtimer_clock_base *base = timer->base;

- spin_lock_irqsave(&base->lock, *flags);
+ spin_lock_irqsave(&base->cpu_base->lock, *flags);

return base;
}
@@ -300,7 +305,7 @@ void hrtimer_notify_resume(void)
static inline
void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
{
- spin_unlock_irqrestore(&timer->base->lock, *flags);
+ spin_unlock_irqrestore(&timer->base->cpu_base->lock, *flags);
}

/**
@@ -350,7 +355,8 @@ hrtimer_forward(struct hrtimer *timer, k
* The timer is inserted in expiry order. Insertion into the
* red black tree is O(log(n)). Must hold the base lock.
*/
-static void enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
+static void enqueue_hrtimer(struct hrtimer *timer,
+ struct hrtimer_clock_base *base)
{
struct rb_node **link = &base->active.rb_node;
struct rb_node *parent = NULL;
@@ -389,7 +395,8 @@ static void enqueue_hrtimer(struct hrtim
*
* Caller must hold the base lock.
*/
-static void __remove_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
+static void __remove_hrtimer(struct hrtimer *timer,
+ struct hrtimer_clock_base *base)
{
/*
* Remove the timer from the rbtree and replace the
@@ -405,7 +412,7 @@ static void __remove_hrtimer(struct hrti
* remove hrtimer, called with base lock held
*/
static inline int
-remove_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
+remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base)
{
if (hrtimer_active(timer)) {
__remove_hrtimer(timer, base);
@@ -427,7 +434,7 @@ remove_hrtimer(struct hrtimer *timer, st
int
hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
{
- struct hrtimer_base *base, *new_base;
+ struct hrtimer_clock_base *base, *new_base;
unsigned long flags;
int ret;

@@ -474,13 +481,13 @@ EXPORT_SYMBOL_GPL(hrtimer_start);
*/
int hrtimer_try_to_cancel(struct hrtimer *timer)
{
- struct hrtimer_base *base;
+ struct hrtimer_clock_base *base;
unsigned long flags;
int ret = -1;

base = lock_hrtimer_base(timer, &flags);

- if (base->curr_timer != timer)
+ if (base->cpu_base->curr_timer != timer)
ret = remove_hrtimer(timer, base);

unlock_hrtimer_base(timer, &flags);
@@ -516,7 +523,7 @@ EXPORT_SYMBOL_GPL(hrtimer_cancel);
*/
ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
{
- struct hrtimer_base *base;
+ struct hrtimer_clock_base *base;
unsigned long flags;
ktime_t rem;

@@ -537,26 +544,29 @@ EXPORT_SYMBOL_GPL(hrtimer_get_remaining)
*/
ktime_t hrtimer_get_next_event(void)
{
- struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
+ struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
+ struct hrtimer_clock_base *base = cpu_base->clock_base;
ktime_t delta, mindelta = { .tv64 = KTIME_MAX };
unsigned long flags;
int i;

- for (i = 0; i < MAX_HRTIMER_BASES; i++, base++) {
+ spin_lock_irqsave(&cpu_base->lock, flags);
+
+ for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
struct hrtimer *timer;

- spin_lock_irqsave(&base->lock, flags);
- if (!base->first) {
- spin_unlock_irqrestore(&base->lock, flags);
+ if (!base->first)
continue;
- }
+
timer = rb_entry(base->first, struct hrtimer, node);
delta.tv64 = timer->expires.tv64;
- spin_unlock_irqrestore(&base->lock, flags);
delta = ktime_sub(delta, base->get_time());
if (delta.tv64 < mindelta.tv64)
mindelta.tv64 = delta.tv64;
}
+
+ spin_unlock_irqrestore(&cpu_base->lock, flags);
+
if (mindelta.tv64 < 0)
mindelta.tv64 = 0;
return mindelta;
@@ -572,16 +582,16 @@ ktime_t hrtimer_get_next_event(void)
void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
enum hrtimer_mode mode)
{
- struct hrtimer_base *bases;
+ struct hrtimer_cpu_base *cpu_base;

memset(timer, 0, sizeof(struct hrtimer));

- bases = __raw_get_cpu_var(hrtimer_bases);
+ cpu_base = &__raw_get_cpu_var(hrtimer_bases);

if (clock_id == CLOCK_REALTIME && mode != HRTIMER_ABS)
clock_id = CLOCK_MONOTONIC;

- timer->base = &bases[clock_id];
+ timer->base = &cpu_base->clock_base[clock_id];
rb_set_parent(&timer->node, &timer->node);
}
EXPORT_SYMBOL_GPL(hrtimer_init);
@@ -596,10 +606,10 @@ EXPORT_SYMBOL_GPL(hrtimer_init);
*/
int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
{
- struct hrtimer_base *bases;
+ struct hrtimer_cpu_base *cpu_base;

- bases = __raw_get_cpu_var(hrtimer_bases);
- *tp = ktime_to_timespec(bases[which_clock].resolution);
+ cpu_base = &__raw_get_cpu_var(hrtimer_bases);
+ *tp = ktime_to_timespec(cpu_base->clock_base[which_clock].resolution);

return 0;
}
@@ -608,9 +618,11 @@ EXPORT_SYMBOL_GPL(hrtimer_get_res);
/*
* Expire the per base hrtimer-queue:
*/
-static inline void run_hrtimer_queue(struct hrtimer_base *base)
+static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
+ int index)
{
struct rb_node *node;
+ struct hrtimer_clock_base *base = &cpu_base->clock_base[index];

if (!base->first)
return;
@@ -618,7 +630,7 @@ static inline void run_hrtimer_queue(str
if (base->get_softirq_time)
base->softirq_time = base->get_softirq_time();

- spin_lock_irq(&base->lock);
+ spin_lock_irq(&cpu_base->lock);

while ((node = base->first)) {
struct hrtimer *timer;
@@ -630,21 +642,21 @@ static inline void run_hrtimer_queue(str
break;

fn = timer->function;
- set_curr_timer(base, timer);
+ set_curr_timer(cpu_base, timer);
__remove_hrtimer(timer, base);
- spin_unlock_irq(&base->lock);
+ spin_unlock_irq(&cpu_base->lock);

restart = fn(timer);

- spin_lock_irq(&base->lock);
+ spin_lock_irq(&cpu_base->lock);

if (restart != HRTIMER_NORESTART) {
BUG_ON(hrtimer_active(timer));
enqueue_hrtimer(timer, base);
}
}
- set_curr_timer(base, NULL);
- spin_unlock_irq(&base->lock);
+ set_curr_timer(cpu_base, NULL);
+ spin_unlock_irq(&cpu_base->lock);
}

/*
@@ -652,13 +664,13 @@ static inline void run_hrtimer_queue(str
*/
void hrtimer_run_queues(void)
{
- struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
+ struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
int i;

- hrtimer_get_softirq_time(base);
+ hrtimer_get_softirq_time(cpu_base);

- for (i = 0; i < MAX_HRTIMER_BASES; i++)
- run_hrtimer_queue(&base[i]);
+ for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
+ run_hrtimer_queue(cpu_base, i);
}

/*
@@ -787,19 +799,21 @@ sys_nanosleep(struct timespec __user *rq
*/
static void __devinit init_hrtimers_cpu(int cpu)
{
- struct hrtimer_base *base = per_cpu(hrtimer_bases, cpu);
+ struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
int i;

- for (i = 0; i < MAX_HRTIMER_BASES; i++, base++) {
- spin_lock_init(&base->lock);
- lockdep_set_class(&base->lock, &base->lock_key);
- }
+ spin_lock_init(&cpu_base->lock);
+ lockdep_set_class(&cpu_base->lock, &cpu_base->lock_key);
+
+ for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
+ cpu_base->clock_base[i].cpu_base = cpu_base;
+
}

#ifdef CONFIG_HOTPLUG_CPU

-static void migrate_hrtimer_list(struct hrtimer_base *old_base,
- struct hrtimer_base *new_base)
+static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
+ struct hrtimer_clock_base *new_base)
{
struct hrtimer *timer;
struct rb_node *node;
@@ -814,29 +828,26 @@ static void migrate_hrtimer_list(struct

static void migrate_hrtimers(int cpu)
{
- struct hrtimer_base *old_base, *new_base;
+ struct hrtimer_cpu_base *old_base, *new_base;
int i;

BUG_ON(cpu_online(cpu));
- old_base = per_cpu(hrtimer_bases, cpu);
- new_base = get_cpu_var(hrtimer_bases);
+ old_base = &per_cpu(hrtimer_bases, cpu);
+ new_base = &get_cpu_var(hrtimer_bases);

local_irq_disable();

- for (i = 0; i < MAX_HRTIMER_BASES; i++) {
-
- spin_lock(&new_base->lock);
- spin_lock(&old_base->lock);
+ spin_lock(&new_base->lock);
+ spin_lock(&old_base->lock);

+ for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
BUG_ON(old_base->curr_timer);

- migrate_hrtimer_list(old_base, new_base);
-
- spin_unlock(&old_base->lock);
- spin_unlock(&new_base->lock);
- old_base++;
- new_base++;
+ migrate_hrtimer_list(&old_base->clock_base[i],
+ &new_base->clock_base[i]);
}
+ spin_unlock(&old_base->lock);
+ spin_unlock(&new_base->lock);

local_irq_enable();
put_cpu_var(hrtimer_bases);

--

-
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