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authorThomas Gleixner <tglx@linutronix.de>2018-01-14 23:30:51 +0100
committerIngo Molnar <mingo@kernel.org>2018-01-16 02:35:44 +0100
commitae67badaa1643253998cb21d5782e4ea7c231a29 (patch)
tree9d12382a6e79d9d6420796d2cca2c6853b9aeed2 /kernel
parent57957fb519449803df30d10da433c27aaad17fa5 (diff)
hrtimer: Optimize the hrtimer code by using static keys for migration_enable/nohz_active
The hrtimer_cpu_base::migration_enable and ::nohz_active fields were originally introduced to avoid accessing global variables for these decisions. Still that results in a (cache hot) load and conditional branch, which can be avoided by using static keys. Implement it with static keys and optimize for the most critical case of high performance networking which tends to disable the timer migration functionality. No change in functionality. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Anna-Maria Gleixner <anna-maria@linutronix.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: keescook@chromium.org Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1801142327490.2371@nanos Link: https://lkml.kernel.org/r/20171221104205.7269-2-anna-maria@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/hrtimer.c17
-rw-r--r--kernel/time/tick-internal.h19
-rw-r--r--kernel/time/tick-sched.c2
-rw-r--r--kernel/time/timer.c83
4 files changed, 60 insertions, 61 deletions
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index d32520840fde..1d06d2bde733 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -178,23 +178,16 @@ hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
#endif
}
-#ifdef CONFIG_NO_HZ_COMMON
-static inline
-struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base,
- int pinned)
-{
- if (pinned || !base->migration_enabled)
- return base;
- return &per_cpu(hrtimer_bases, get_nohz_timer_target());
-}
-#else
static inline
struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base,
int pinned)
{
+#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+ if (static_branch_likely(&timers_migration_enabled) && !pinned)
+ return &per_cpu(hrtimer_bases, get_nohz_timer_target());
+#endif
return base;
}
-#endif
/*
* We switch the timer base to a power-optimized selected CPU target,
@@ -969,7 +962,7 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
* Kick to reschedule the next tick to handle the new timer
* on dynticks target.
*/
- if (new_base->cpu_base->nohz_active)
+ if (is_timers_nohz_active())
wake_up_nohz_cpu(new_base->cpu_base->cpu);
} else {
hrtimer_reprogram(timer, new_base);
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index f8e1845aa464..f690628e068c 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -150,14 +150,19 @@ static inline void tick_nohz_init(void) { }
#ifdef CONFIG_NO_HZ_COMMON
extern unsigned long tick_nohz_active;
-#else
+extern void timers_update_nohz(void);
+extern struct static_key_false timers_nohz_active;
+static inline bool is_timers_nohz_active(void)
+{
+ return static_branch_likely(&timers_nohz_active);
+}
+# ifdef CONFIG_SMP
+extern struct static_key_false timers_migration_enabled;
+# endif
+#else /* CONFIG_NO_HZ_COMMON */
+static inline void timers_update_nohz(void) { }
#define tick_nohz_active (0)
-#endif
-
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
-extern void timers_update_migration(bool update_nohz);
-#else
-static inline void timers_update_migration(bool update_nohz) { }
+static inline bool is_timers_nohz_active(void) { return false; }
#endif
DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f7cc7abfcf25..29a5733eff83 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1107,7 +1107,7 @@ static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
ts->nohz_mode = mode;
/* One update is enough */
if (!test_and_set_bit(0, &tick_nohz_active))
- timers_update_migration(true);
+ timers_update_nohz();
}
/**
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 0bcf00e3ce48..d530f72b32f9 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -200,8 +200,6 @@ struct timer_base {
unsigned long clk;
unsigned long next_expiry;
unsigned int cpu;
- bool migration_enabled;
- bool nohz_active;
bool is_idle;
bool must_forward_clk;
DECLARE_BITMAP(pending_map, WHEEL_SIZE);
@@ -210,45 +208,57 @@ struct timer_base {
static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+#ifdef CONFIG_NO_HZ_COMMON
+
+DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
+static DEFINE_MUTEX(timer_keys_mutex);
+
+static void timer_update_keys(struct work_struct *work);
+static DECLARE_WORK(timer_update_work, timer_update_keys);
+
+#ifdef CONFIG_SMP
unsigned int sysctl_timer_migration = 1;
-void timers_update_migration(bool update_nohz)
+DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
+
+static void timers_update_migration(void)
{
- bool on = sysctl_timer_migration && tick_nohz_active;
- unsigned int cpu;
+ if (sysctl_timer_migration && tick_nohz_active)
+ static_branch_enable(&timers_migration_enabled);
+ else
+ static_branch_disable(&timers_migration_enabled);
+}
+#else
+static inline void timers_update_migration(void) { }
+#endif /* !CONFIG_SMP */
- /* Avoid the loop, if nothing to update */
- if (this_cpu_read(timer_bases[BASE_STD].migration_enabled) == on)
- return;
+static void timer_update_keys(struct work_struct *work)
+{
+ mutex_lock(&timer_keys_mutex);
+ timers_update_migration();
+ static_branch_enable(&timers_nohz_active);
+ mutex_unlock(&timer_keys_mutex);
+}
- for_each_possible_cpu(cpu) {
- per_cpu(timer_bases[BASE_STD].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_DEF].nohz_active, cpu) = true;
- per_cpu(hrtimer_bases.nohz_active, cpu) = true;
- }
+void timers_update_nohz(void)
+{
+ schedule_work(&timer_update_work);
}
int timer_migration_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
- static DEFINE_MUTEX(mutex);
int ret;
- mutex_lock(&mutex);
+ mutex_lock(&timer_keys_mutex);
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
if (!ret && write)
- timers_update_migration(false);
- mutex_unlock(&mutex);
+ timers_update_migration();
+ mutex_unlock(&timer_keys_mutex);
return ret;
}
-#endif
+#endif /* NO_HZ_COMMON */
static unsigned long round_jiffies_common(unsigned long j, int cpu,
bool force_up)
@@ -534,7 +544,7 @@ __internal_add_timer(struct timer_base *base, struct timer_list *timer)
static void
trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
{
- if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active)
+ if (!is_timers_nohz_active())
return;
/*
@@ -849,21 +859,20 @@ static inline struct timer_base *get_timer_base(u32 tflags)
return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
}
-#ifdef CONFIG_NO_HZ_COMMON
static inline struct timer_base *
get_target_base(struct timer_base *base, unsigned tflags)
{
-#ifdef CONFIG_SMP
- if ((tflags & TIMER_PINNED) || !base->migration_enabled)
- return get_timer_this_cpu_base(tflags);
- return get_timer_cpu_base(tflags, get_nohz_timer_target());
-#else
- return get_timer_this_cpu_base(tflags);
+#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+ if (static_branch_likely(&timers_migration_enabled) &&
+ !(tflags & TIMER_PINNED))
+ return get_timer_cpu_base(tflags, get_nohz_timer_target());
#endif
+ return get_timer_this_cpu_base(tflags);
}
static inline void forward_timer_base(struct timer_base *base)
{
+#ifdef CONFIG_NO_HZ_COMMON
unsigned long jnow;
/*
@@ -887,16 +896,8 @@ static inline void forward_timer_base(struct timer_base *base)
base->clk = jnow;
else
base->clk = base->next_expiry;
-}
-#else
-static inline struct timer_base *
-get_target_base(struct timer_base *base, unsigned tflags)
-{
- return get_timer_this_cpu_base(tflags);
-}
-
-static inline void forward_timer_base(struct timer_base *base) { }
#endif
+}
/*