sched: Add a timer to handle CFS bandwidth refresh

This patch adds a per-task_group timer which handles the refresh of the global
CFS bandwidth pool.

Since the RT pool is using a similar timer there's some small refactoring to
share this support.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110721184757.277271273@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 123 insertions, 24 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 35561c63a490..34bf8e6db9af 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -196,10 +196,28 @@ static inline int rt_bandwidth_enabled(void)
         return sysctl_sched_rt_runtime >= 0;
 }
 
-static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+static void start_bandwidth_timer(struct hrtimer *period_timer, ktime_t period)
 {
-        ktime_t now;
+        unsigned long delta;
+        ktime_t soft, hard, now;
 
+        for (;;) {
+                if (hrtimer_active(period_timer))
+                        break;
+
+                now = hrtimer_cb_get_time(period_timer);
+                hrtimer_forward(period_timer, now, period);
+
+                soft = hrtimer_get_softexpires(period_timer);
+                hard = hrtimer_get_expires(period_timer);
+                delta = ktime_to_ns(ktime_sub(hard, soft));
+                __hrtimer_start_range_ns(period_timer, soft, delta,
+                                         HRTIMER_MODE_ABS_PINNED, 0);
+        }
+}
+
+static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
         if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
                 return;
 
@@ -207,22 +225,7 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
                 return;
 
         raw_spin_lock(&rt_b->rt_runtime_lock);
-        for (;;) {
-                unsigned long delta;
-                ktime_t soft, hard;
-
-                if (hrtimer_active(&rt_b->rt_period_timer))
-                        break;
-
-                now = hrtimer_cb_get_time(&rt_b->rt_period_timer);
-                hrtimer_forward(&rt_b->rt_period_timer, now, rt_b->rt_period);
-
-                soft = hrtimer_get_softexpires(&rt_b->rt_period_timer);
-                hard = hrtimer_get_expires(&rt_b->rt_period_timer);
-                delta = ktime_to_ns(ktime_sub(hard, soft));
-                __hrtimer_start_range_ns(&rt_b->rt_period_timer, soft, delta,
-                                HRTIMER_MODE_ABS_PINNED, 0);
-        }
+        start_bandwidth_timer(&rt_b->rt_period_timer, rt_b->rt_period);
         raw_spin_unlock(&rt_b->rt_runtime_lock);
 }
 
@@ -253,6 +256,9 @@ struct cfs_bandwidth {
         ktime_t period;
         u64 quota, runtime;
         s64 hierarchal_quota;
+
+        int idle, timer_active;
+        struct hrtimer period_timer;
 #endif
 };
 
@@ -403,6 +409,28 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 }
 
 static inline u64 default_cfs_period(void);
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun);
+
+static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
+{
+        struct cfs_bandwidth *cfs_b =
+                container_of(timer, struct cfs_bandwidth, period_timer);
+        ktime_t now;
+        int overrun;
+        int idle = 0;
+
+        for (;;) {
+                now = hrtimer_cb_get_time(timer);
+                overrun = hrtimer_forward(timer, now, cfs_b->period);
+
+                if (!overrun)
+                        break;
+
+                idle = do_sched_cfs_period_timer(cfs_b, overrun);
+        }
+
+        return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
+}
 
 static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 {
@@ -410,6 +438,9 @@ static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
         cfs_b->runtime = 0;
         cfs_b->quota = RUNTIME_INF;
         cfs_b->period = ns_to_ktime(default_cfs_period());
+
+        hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        cfs_b->period_timer.function = sched_cfs_period_timer;
 }
 
 static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
@@ -417,8 +448,34 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
         cfs_rq->runtime_enabled = 0;
 }
 
+/* requires cfs_b->lock, may release to reprogram timer */
+static void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
+{
+        /*
+         * The timer may be active because we're trying to set a new bandwidth
+         * period or because we're racing with the tear-down path
+         * (timer_active==0 becomes visible before the hrtimer call-back
+         * terminates).  In either case we ensure that it's re-programmed
+         */
+        while (unlikely(hrtimer_active(&cfs_b->period_timer))) {
+                raw_spin_unlock(&cfs_b->lock);
+                /* ensure cfs_b->lock is available while we wait */
+                hrtimer_cancel(&cfs_b->period_timer);
+
+                raw_spin_lock(&cfs_b->lock);
+                /* if someone else restarted the timer then we're done */
+                if (cfs_b->timer_active)
+                        return;
+        }
+
+        cfs_b->timer_active = 1;
+        start_bandwidth_timer(&cfs_b->period_timer, cfs_b->period);
+}
+
 static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
-{}
+{
+        hrtimer_cancel(&cfs_b->period_timer);
+}
 #else
 static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
 static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
@@ -9078,7 +9135,7 @@ static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
 
 static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
 {
-        int i, ret = 0;
+        int i, ret = 0, runtime_enabled;
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
 
         if (tg == &root_task_group)
@@ -9105,10 +9162,18 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
         if (ret)
                 goto out_unlock;
 
+        runtime_enabled = quota != RUNTIME_INF;
         raw_spin_lock_irq(&cfs_b->lock);
         cfs_b->period = ns_to_ktime(period);
         cfs_b->quota = quota;
         cfs_b->runtime = quota;
+
+        /* restart the period timer (if active) to handle new period expiry */
+        if (runtime_enabled && cfs_b->timer_active) {
+                /* force a reprogram */
+                cfs_b->timer_active = 0;
+                __start_cfs_bandwidth(cfs_b);
+        }
         raw_spin_unlock_irq(&cfs_b->lock);
 
         for_each_possible_cpu(i) {
@@ -9116,7 +9181,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
                 struct rq *rq = rq_of(cfs_rq);
 
                 raw_spin_lock_irq(&rq->lock);
-                cfs_rq->runtime_enabled = quota != RUNTIME_INF;
+                cfs_rq->runtime_enabled = runtime_enabled;
                 cfs_rq->runtime_remaining = 0;
                 raw_spin_unlock_irq(&rq->lock);
         }
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9502aa899f73..af73a8a85eef 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1284,9 +1284,16 @@ static void assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
         raw_spin_lock(&cfs_b->lock);
         if (cfs_b->quota == RUNTIME_INF)
                 amount = min_amount;
-        else if (cfs_b->runtime > 0) {
-                amount = min(cfs_b->runtime, min_amount);
-                cfs_b->runtime -= amount;
+        else {
+                /* ensure bandwidth timer remains active under consumption */
+                if (!cfs_b->timer_active)
+                        __start_cfs_bandwidth(cfs_b);
+
+                if (cfs_b->runtime > 0) {
+                        amount = min(cfs_b->runtime, min_amount);
+                        cfs_b->runtime -= amount;
+                        cfs_b->idle = 0;
+                }
         }
         raw_spin_unlock(&cfs_b->lock);
 
@@ -1315,6 +1322,33 @@ static __always_inline void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
         __account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
 
+/*
+ * Responsible for refilling a task_group's bandwidth and unthrottling its
+ * cfs_rqs as appropriate. If there has been no activity within the last
+ * period the timer is deactivated until scheduling resumes; cfs_b->idle is
+ * used to track this state.
+ */
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
+{
+        int idle = 1;
+
+        raw_spin_lock(&cfs_b->lock);
+        /* no need to continue the timer with no bandwidth constraint */
+        if (cfs_b->quota == RUNTIME_INF)
+                goto out_unlock;
+
+        idle = cfs_b->idle;
+        cfs_b->runtime = cfs_b->quota;
+
+        /* mark as potentially idle for the upcoming period */
+        cfs_b->idle = 1;
+out_unlock:
+        if (idle)
+                cfs_b->timer_active = 0;
+        raw_spin_unlock(&cfs_b->lock);
+
+        return idle;
+}
 #else
 static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
                                      unsigned long delta_exec) {}