timer: Replace timer base by a cpu index
Instead of storing a pointer to the per cpu tvec_base we can simply
cache a CPU index in the timer_list and use that to get hold of the
correct per cpu tvec_base. This is only used in lock_timer_base() and
the slightly larger code is peanuts versus the spinlock operation and
the d-cache foot print of the timer wheel.
Aside of that this allows to get rid of following nuisances:
- boot_tvec_base
That statically allocated 4k bss data is just kept around so the
timer has a home when it gets statically initialized. It serves no
other purpose.
With the CPU index we assign the timer to CPU0 at static
initialization time and therefor can avoid the whole boot_tvec_base
dance. That also simplifies the init code, which just can use the
per cpu base.
Before:
text data bss dec hex filename
17491 9201 4160 30852 7884 ../build/kernel/time/timer.o
After:
text data bss dec hex filename
17440 9193 0 26633 6809 ../build/kernel/time/timer.o
- Overloading the base pointer with various flags
The CPU index has enough space to hold the flags (deferrable,
irqsafe) so we can get rid of the extra masking and bit fiddling
with the base pointer.
As a benefit we reduce the size of struct timer_list on 64 bit
machines. 4 - 8 bytes, a size reduction up to 15% per struct timer_list,
which is a real win as we have tons of them embedded in other structs.
This changes also the newly added deferrable printout of the timer
start trace point to capture and print all timer->flags, which allows
us to decode the target cpu of the timer as well.
We might have used bitfields for this, but that would change the
static initializers and the init function for no value to accomodate
big endian bitfields.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Joonwoo Park <joonwoop@codeaurora.org>
Cc: Wenbo Wang <wenbo.wang@memblaze.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Badhri Jagan Sridharan <Badhri@google.com>
Link: http://lkml.kernel.org/r/20150526224511.950084301@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 3a5e0c8..1540af9 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -92,43 +92,8 @@
struct tvec tv5;
} ____cacheline_aligned;
-/*
- * __TIMER_INITIALIZER() needs to set ->base to a valid pointer (because we've
- * made NULL special, hint: lock_timer_base()) and we cannot get a compile time
- * pointer to per-cpu entries because we don't know where we'll map the section,
- * even for the boot cpu.
- *
- * And so we use boot_tvec_bases for boot CPU and per-cpu __tvec_bases for the
- * rest of them.
- */
-struct tvec_base boot_tvec_bases;
-EXPORT_SYMBOL(boot_tvec_bases);
-static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;
-
-/* Functions below help us manage 'deferrable' flag */
-static inline unsigned int tbase_get_deferrable(struct tvec_base *base)
-{
- return ((unsigned int)(unsigned long)base & TIMER_DEFERRABLE);
-}
-
-static inline unsigned int tbase_get_irqsafe(struct tvec_base *base)
-{
- return ((unsigned int)(unsigned long)base & TIMER_IRQSAFE);
-}
-
-static inline struct tvec_base *tbase_get_base(struct tvec_base *base)
-{
- return ((struct tvec_base *)((unsigned long)base & ~TIMER_FLAG_MASK));
-}
-
-static inline void
-timer_set_base(struct timer_list *timer, struct tvec_base *new_base)
-{
- unsigned long flags = (unsigned long)timer->base & TIMER_FLAG_MASK;
-
- timer->base = (struct tvec_base *)((unsigned long)(new_base) | flags);
-}
+static DEFINE_PER_CPU(struct tvec_base, tvec_bases);
static unsigned long round_jiffies_common(unsigned long j, int cpu,
bool force_up)
@@ -403,7 +368,7 @@
/*
* Update base->active_timers and base->next_timer
*/
- if (!tbase_get_deferrable(timer->base)) {
+ if (!(timer->flags & TIMER_DEFERRABLE)) {
if (!base->active_timers++ ||
time_before(timer->expires, base->next_timer))
base->next_timer = timer->expires;
@@ -422,7 +387,7 @@
* require special care against races with idle_cpu(), lets deal
* with that later.
*/
- if (!tbase_get_deferrable(timer->base) || tick_nohz_full_cpu(base->cpu))
+ if (!(timer->flags & TIMER_DEFERRABLE) || tick_nohz_full_cpu(base->cpu))
wake_up_nohz_cpu(base->cpu);
}
@@ -443,7 +408,7 @@
if (likely(!timer->start_site))
return;
- if (unlikely(tbase_get_deferrable(timer->base)))
+ if (unlikely(timer->flags & TIMER_DEFERRABLE))
flag |= TIMER_STATS_FLAG_DEFERRABLE;
timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
@@ -636,7 +601,7 @@
debug_activate(struct timer_list *timer, unsigned long expires)
{
debug_timer_activate(timer);
- trace_timer_start(timer, expires, tbase_get_deferrable(timer->base));
+ trace_timer_start(timer, expires, timer->flags);
}
static inline void debug_deactivate(struct timer_list *timer)
@@ -653,10 +618,8 @@
static void do_init_timer(struct timer_list *timer, unsigned int flags,
const char *name, struct lock_class_key *key)
{
- struct tvec_base *base = raw_cpu_read(tvec_bases);
-
timer->entry.pprev = NULL;
- timer->base = (void *)((unsigned long)base | flags);
+ timer->flags = flags | raw_smp_processor_id();
timer->slack = -1;
#ifdef CONFIG_TIMER_STATS
timer->start_site = NULL;
@@ -701,7 +664,7 @@
detach_expired_timer(struct timer_list *timer, struct tvec_base *base)
{
detach_timer(timer, true);
- if (!tbase_get_deferrable(timer->base))
+ if (!(timer->flags & TIMER_DEFERRABLE))
base->active_timers--;
base->all_timers--;
}
@@ -713,7 +676,7 @@
return 0;
detach_timer(timer, clear_pending);
- if (!tbase_get_deferrable(timer->base)) {
+ if (!(timer->flags & TIMER_DEFERRABLE)) {
base->active_timers--;
if (timer->expires == base->next_timer)
base->next_timer = base->timer_jiffies;
@@ -732,24 +695,22 @@
* So __run_timers/migrate_timers can safely modify all timers which could
* be found on ->tvX lists.
*
- * When the timer's base is locked, and the timer removed from list, it is
- * possible to set timer->base = NULL and drop the lock: the timer remains
- * locked.
+ * When the timer's base is locked and removed from the list, the
+ * TIMER_MIGRATING flag is set, FIXME
*/
static struct tvec_base *lock_timer_base(struct timer_list *timer,
unsigned long *flags)
__acquires(timer->base->lock)
{
- struct tvec_base *base;
-
for (;;) {
- struct tvec_base *prelock_base = timer->base;
- base = tbase_get_base(prelock_base);
- if (likely(base != NULL)) {
+ u32 tf = timer->flags;
+ struct tvec_base *base;
+
+ if (!(tf & TIMER_MIGRATING)) {
+ base = per_cpu_ptr(&tvec_bases, tf & TIMER_CPUMASK);
spin_lock_irqsave(&base->lock, *flags);
- if (likely(prelock_base == timer->base))
+ if (timer->flags == tf)
return base;
- /* The timer has migrated to another CPU */
spin_unlock_irqrestore(&base->lock, *flags);
}
cpu_relax();
@@ -776,7 +737,7 @@
debug_activate(timer, expires);
cpu = get_nohz_timer_target(pinned);
- new_base = per_cpu(tvec_bases, cpu);
+ new_base = per_cpu_ptr(&tvec_bases, cpu);
if (base != new_base) {
/*
@@ -788,11 +749,12 @@
*/
if (likely(base->running_timer != timer)) {
/* See the comment in lock_timer_base() */
- timer_set_base(timer, NULL);
+ timer->flags |= TIMER_MIGRATING;
+
spin_unlock(&base->lock);
base = new_base;
spin_lock(&base->lock);
- timer_set_base(timer, base);
+ timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
}
}
@@ -954,13 +916,13 @@
*/
void add_timer_on(struct timer_list *timer, int cpu)
{
- struct tvec_base *base = per_cpu(tvec_bases, cpu);
+ struct tvec_base *base = per_cpu_ptr(&tvec_bases, cpu);
unsigned long flags;
timer_stats_timer_set_start_info(timer);
BUG_ON(timer_pending(timer) || !timer->function);
spin_lock_irqsave(&base->lock, flags);
- timer_set_base(timer, base);
+ timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
debug_activate(timer, timer->expires);
internal_add_timer(base, timer);
spin_unlock_irqrestore(&base->lock, flags);
@@ -1025,8 +987,6 @@
EXPORT_SYMBOL(try_to_del_timer_sync);
#ifdef CONFIG_SMP
-static DEFINE_PER_CPU(struct tvec_base, __tvec_bases);
-
/**
* del_timer_sync - deactivate a timer and wait for the handler to finish.
* @timer: the timer to be deactivated
@@ -1081,7 +1041,7 @@
* don't use it in hardirq context, because it
* could lead to deadlock.
*/
- WARN_ON(in_irq() && !tbase_get_irqsafe(timer->base));
+ WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
for (;;) {
int ret = try_to_del_timer_sync(timer);
if (ret >= 0)
@@ -1106,7 +1066,6 @@
* don't have to detach them individually.
*/
hlist_for_each_entry_safe(timer, tmp, &tv_list, entry) {
- BUG_ON(tbase_get_base(timer->base) != base);
/* No accounting, while moving them */
__internal_add_timer(base, timer);
}
@@ -1202,7 +1161,7 @@
timer = hlist_entry(head->first, struct timer_list, entry);
fn = timer->function;
data = timer->data;
- irqsafe = tbase_get_irqsafe(timer->base);
+ irqsafe = timer->flags & TIMER_IRQSAFE;
timer_stats_account_timer(timer);
@@ -1242,7 +1201,7 @@
index = slot = timer_jiffies & TVR_MASK;
do {
hlist_for_each_entry(nte, base->tv1.vec + slot, entry) {
- if (tbase_get_deferrable(nte->base))
+ if (nte->flags & TIMER_DEFERRABLE)
continue;
found = 1;
@@ -1273,7 +1232,7 @@
index = slot = timer_jiffies & TVN_MASK;
do {
hlist_for_each_entry(nte, varp->vec + slot, entry) {
- if (tbase_get_deferrable(nte->base))
+ if (nte->flags & TIMER_DEFERRABLE)
continue;
found = 1;
@@ -1343,7 +1302,7 @@
*/
u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
{
- struct tvec_base *base = __this_cpu_read(tvec_bases);
+ struct tvec_base *base = this_cpu_ptr(&tvec_bases);
u64 expires = KTIME_MAX;
unsigned long nextevt;
@@ -1395,7 +1354,7 @@
*/
static void run_timer_softirq(struct softirq_action *h)
{
- struct tvec_base *base = __this_cpu_read(tvec_bases);
+ struct tvec_base *base = this_cpu_ptr(&tvec_bases);
if (time_after_eq(jiffies, base->timer_jiffies))
__run_timers(base);
@@ -1534,12 +1493,13 @@
static void migrate_timer_list(struct tvec_base *new_base, struct hlist_head *head)
{
struct timer_list *timer;
+ int cpu = new_base->cpu;
while (!hlist_empty(head)) {
timer = hlist_entry(head->first, struct timer_list, entry);
/* We ignore the accounting on the dying cpu */
detach_timer(timer, false);
- timer_set_base(timer, new_base);
+ timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
internal_add_timer(new_base, timer);
}
}
@@ -1551,8 +1511,8 @@
int i;
BUG_ON(cpu_online(cpu));
- old_base = per_cpu(tvec_bases, cpu);
- new_base = get_cpu_var(tvec_bases);
+ old_base = per_cpu_ptr(&tvec_bases, cpu);
+ new_base = this_cpu_ptr(&tvec_bases);
/*
* The caller is globally serialized and nobody else
* takes two locks at once, deadlock is not possible.
@@ -1576,7 +1536,6 @@
spin_unlock(&old_base->lock);
spin_unlock_irq(&new_base->lock);
- put_cpu_var(tvec_bases);
}
static int timer_cpu_notify(struct notifier_block *self,
@@ -1602,12 +1561,11 @@
static inline void timer_register_cpu_notifier(void) { }
#endif /* CONFIG_HOTPLUG_CPU */
-static void __init init_timer_cpu(struct tvec_base *base, int cpu)
+static void __init init_timer_cpu(int cpu)
{
- BUG_ON(base != tbase_get_base(base));
+ struct tvec_base *base = per_cpu_ptr(&tvec_bases, cpu);
base->cpu = cpu;
- per_cpu(tvec_bases, cpu) = base;
spin_lock_init(&base->lock);
base->timer_jiffies = jiffies;
@@ -1616,27 +1574,14 @@
static void __init init_timer_cpus(void)
{
- struct tvec_base *base;
- int local_cpu = smp_processor_id();
int cpu;
- for_each_possible_cpu(cpu) {
- if (cpu == local_cpu)
- base = &boot_tvec_bases;
-#ifdef CONFIG_SMP
- else
- base = per_cpu_ptr(&__tvec_bases, cpu);
-#endif
-
- init_timer_cpu(base, cpu);
- }
+ for_each_possible_cpu(cpu)
+ init_timer_cpu(cpu);
}
void __init init_timers(void)
{
- /* ensure there are enough low bits for flags in timer->base pointer */
- BUILD_BUG_ON(__alignof__(struct tvec_base) & TIMER_FLAG_MASK);
-
init_timer_cpus();
init_timer_stats();
timer_register_cpu_notifier();