Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched, x86: Avoid unnecessary overflow in sched_clock
  sched: Fix buglet in return_cfs_rq_runtime()
  sched: Avoid SMT siblings in select_idle_sibling() if possible
  sched: Set the command name of the idle tasks in SMP kernels
  sched, rt: Provide means of disabling cross-cpu bandwidth sharing
  sched: Document wait_for_completion_*() return values
  sched_fair: Fix a typo in the comment describing update_sd_lb_stats
  sched: Add a comment to effective_load() since it's a pain

4 files changed, 146 insertions, 34 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 0e9344a71be3..d6b149ccf925 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -71,6 +71,7 @@
 #include <linux/ctype.h>
 #include <linux/ftrace.h>
 #include <linux/slab.h>
+#include <linux/init_task.h>
 
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
@@ -4810,6 +4811,9 @@ EXPORT_SYMBOL(wait_for_completion);
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. The timeout is in jiffies. It is not
  * interruptible.
+ *
+ * The return value is 0 if timed out, and positive (at least 1, or number of
+ * jiffies left till timeout) if completed.
  */
 unsigned long __sched
 wait_for_completion_timeout(struct completion *x, unsigned long timeout)
@@ -4824,6 +4828,8 @@ EXPORT_SYMBOL(wait_for_completion_timeout);
  *
  * This waits for completion of a specific task to be signaled. It is
  * interruptible.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if completed.
  */
 int __sched wait_for_completion_interruptible(struct completion *x)
 {
@@ -4841,6 +4847,9 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
  *
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. It is interruptible. The timeout is in jiffies.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if timed out,
+ * positive (at least 1, or number of jiffies left till timeout) if completed.
  */
 long __sched
 wait_for_completion_interruptible_timeout(struct completion *x,
@@ -4856,6 +4865,8 @@ EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);
  *
  * This waits to be signaled for completion of a specific task. It can be
  * interrupted by a kill signal.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if completed.
  */
 int __sched wait_for_completion_killable(struct completion *x)
 {
@@ -4874,6 +4885,9 @@ EXPORT_SYMBOL(wait_for_completion_killable);
  * This waits for either a completion of a specific task to be
  * signaled or for a specified timeout to expire. It can be
  * interrupted by a kill signal. The timeout is in jiffies.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if timed out,
+ * positive (at least 1, or number of jiffies left till timeout) if completed.
  */
 long __sched
 wait_for_completion_killable_timeout(struct completion *x,
@@ -6099,6 +6113,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
          */
         idle->sched_class = &idle_sched_class;
         ftrace_graph_init_idle_task(idle, cpu);
+#if defined(CONFIG_SMP)
+        sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
+#endif
 }
 
 /*
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5c9e67923b7c..a78ed2736ba7 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -772,19 +772,32 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
                 list_del_leaf_cfs_rq(cfs_rq);
 }
 
+static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
+{
+        long tg_weight;
+
+        /*
+         * Use this CPU's actual weight instead of the last load_contribution
+         * to gain a more accurate current total weight. See
+         * update_cfs_rq_load_contribution().
+         */
+        tg_weight = atomic_read(&tg->load_weight);
+        tg_weight -= cfs_rq->load_contribution;
+        tg_weight += cfs_rq->load.weight;
+
+        return tg_weight;
+}
+
 static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
 {
-        long load_weight, load, shares;
+        long tg_weight, load, shares;
 
+        tg_weight = calc_tg_weight(tg, cfs_rq);
         load = cfs_rq->load.weight;
 
-        load_weight = atomic_read(&tg->load_weight);
-        load_weight += load;
-        load_weight -= cfs_rq->load_contribution;
-
         shares = (tg->shares * load);
-        if (load_weight)
-                shares /= load_weight;
+        if (tg_weight)
+                shares /= tg_weight;
 
         if (shares < MIN_SHARES)
                 shares = MIN_SHARES;
@@ -1743,7 +1756,7 @@ static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
-        if (!cfs_rq->runtime_enabled || !cfs_rq->nr_running)
+        if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
                 return;
 
         __return_cfs_rq_runtime(cfs_rq);
@@ -2036,36 +2049,100 @@ static void task_waking_fair(struct task_struct *p)
  * Adding load to a group doesn't make a group heavier, but can cause movement
  * of group shares between cpus. Assuming the shares were perfectly aligned one
  * can calculate the shift in shares.
+ *
+ * Calculate the effective load difference if @wl is added (subtracted) to @tg
+ * on this @cpu and results in a total addition (subtraction) of @wg to the
+ * total group weight.
+ *
+ * Given a runqueue weight distribution (rw_i) we can compute a shares
+ * distribution (s_i) using:
+ *
+ *   s_i = rw_i / \Sum rw_j                                             (1)
+ *
+ * Suppose we have 4 CPUs and our @tg is a direct child of the root group and
+ * has 7 equal weight tasks, distributed as below (rw_i), with the resulting
+ * shares distribution (s_i):
+ *
+ *   rw_i = {   2,   4,   1,   0 }
+ *   s_i  = { 2/7, 4/7, 1/7,   0 }
+ *
+ * As per wake_affine() we're interested in the load of two CPUs (the CPU the
+ * task used to run on and the CPU the waker is running on), we need to
+ * compute the effect of waking a task on either CPU and, in case of a sync
+ * wakeup, compute the effect of the current task going to sleep.
+ *
+ * So for a change of @wl to the local @cpu with an overall group weight change
+ * of @wl we can compute the new shares distribution (s'_i) using:
+ *
+ *   s'_i = (rw_i + @wl) / (@wg + \Sum rw_j)                            (2)
+ *
+ * Suppose we're interested in CPUs 0 and 1, and want to compute the load
+ * differences in waking a task to CPU 0. The additional task changes the
+ * weight and shares distributions like:
+ *
+ *   rw'_i = {   3,   4,   1,   0 }
+ *   s'_i  = { 3/8, 4/8, 1/8,   0 }
+ *
+ * We can then compute the difference in effective weight by using:
+ *
+ *   dw_i = S * (s'_i - s_i)                                            (3)
+ *
+ * Where 'S' is the group weight as seen by its parent.
+ *
+ * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
+ * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
+ * 4/7) times the weight of the group.
  */
 static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 {
         struct sched_entity *se = tg->se[cpu];
 
-        if (!tg->parent)
+        if (!tg->parent)        /* the trivial, non-cgroup case */
                 return wl;
 
         for_each_sched_entity(se) {
-                long lw, w;
+                long w, W;
 
                 tg = se->my_q->tg;
-                w = se->my_q->load.weight;
 
-                /* use this cpu's instantaneous contribution */
-                lw = atomic_read(&tg->load_weight);
-                lw -= se->my_q->load_contribution;
-                lw += w + wg;
+                /*
+                 * W = @wg + \Sum rw_j
+                 */
+                W = wg + calc_tg_weight(tg, se->my_q);
 
-                wl += w;
+                /*
+                 * w = rw_i + @wl
+                 */
+                w = se->my_q->load.weight + wl;
 
-                if (lw > 0 && wl < lw)
-                        wl = (wl * tg->shares) / lw;
+                /*
+                 * wl = S * s'_i; see (2)
+                 */
+                if (W > 0 && w < W)
+                        wl = (w * tg->shares) / W;
                 else
                         wl = tg->shares;
 
-                /* zero point is MIN_SHARES */
+                /*
+                 * Per the above, wl is the new se->load.weight value; since
+                 * those are clipped to [MIN_SHARES, ...) do so now. See
+                 * calc_cfs_shares().
+                 */
                 if (wl < MIN_SHARES)
                         wl = MIN_SHARES;
+
+                /*
+                 * wl = dw_i = S * (s'_i - s_i); see (3)
+                 */
                 wl -= se->load.weight;
+
+                /*
+                 * Recursively apply this logic to all parent groups to compute
+                 * the final effective load change on the root group. Since
+                 * only the @tg group gets extra weight, all parent groups can
+                 * only redistribute existing shares. @wl is the shift in shares
+                 * resulting from this level per the above.
+                 */
                 wg = 0;
         }
 
@@ -2249,7 +2326,8 @@ static int select_idle_sibling(struct task_struct *p, int target)
         int cpu = smp_processor_id();
         int prev_cpu = task_cpu(p);
         struct sched_domain *sd;
-        int i;
+        struct sched_group *sg;
+        int i, smt = 0;
 
         /*
          * If the task is going to be woken-up on this cpu and if it is
@@ -2269,25 +2347,38 @@ static int select_idle_sibling(struct task_struct *p, int target)
          * Otherwise, iterate the domains and find an elegible idle cpu.
          */
         rcu_read_lock();
+again:
         for_each_domain(target, sd) {
-                if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
-                        break;
+                if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
+                        continue;
 
-                for_each_cpu_and(i, sched_domain_span(sd), tsk_cpus_allowed(p)) {
-                        if (idle_cpu(i)) {
-                                target = i;
-                                break;
+                if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
+                        if (!smt) {
+                                smt = 1;
+                                goto again;
                         }
+                        break;
                 }
 
-                /*
-                 * Lets stop looking for an idle sibling when we reached
-                 * the domain that spans the current cpu and prev_cpu.
-                 */
-                if (cpumask_test_cpu(cpu, sched_domain_span(sd)) &&
-                    cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
-                        break;
+                sg = sd->groups;
+                do {
+                        if (!cpumask_intersects(sched_group_cpus(sg),
+                                                tsk_cpus_allowed(p)))
+                                goto next;
+
+                        for_each_cpu(i, sched_group_cpus(sg)) {
+                                if (!idle_cpu(i))
+                                        goto next;
+                        }
+
+                        target = cpumask_first_and(sched_group_cpus(sg),
+                                        tsk_cpus_allowed(p));
+                        goto done;
+next:
+                        sg = sg->next;
+                } while (sg != sd->groups);
         }
+done:
         rcu_read_unlock();
 
         return target;
@@ -3511,7 +3602,7 @@ static bool update_sd_pick_busiest(struct sched_domain *sd,
 }
 
 /**
- * update_sd_lb_stats - Update sched_group's statistics for load balancing.
+ * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
  * @sd: sched_domain whose statistics are to be updated.
  * @this_cpu: Cpu for which load balance is currently performed.
  * @idle: Idle status of this_cpu
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index efa0a7b75dde..84802245abd2 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -67,3 +67,4 @@ SCHED_FEAT(NONTASK_POWER, 1)
 SCHED_FEAT(TTWU_QUEUE, 1)
 
 SCHED_FEAT(FORCE_SD_OVERLAP, 0)
+SCHED_FEAT(RT_RUNTIME_SHARE, 1)
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 056cbd2e2a27..583a1368afe6 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -560,6 +560,9 @@ static int balance_runtime(struct rt_rq *rt_rq)
 {
         int more = 0;
 
+        if (!sched_feat(RT_RUNTIME_SHARE))
+                return more;
+
         if (rt_rq->rt_time > rt_rq->rt_runtime) {
                 raw_spin_unlock(&rt_rq->rt_runtime_lock);
                 more = do_balance_runtime(rt_rq);