higher scheduler load resolution

index 12211e1..c34a718 100644
@@ -788,17 +788,39 @@ enum cpu_idle_type {
 };
 
 /*
- * sched-domains (multiprocessor balancing) declarations:
+ * Increase resolution of nice-level calculations for 64-bit architectures.
+ * The extra resolution improves shares distribution and load balancing of
+ * low-weight task groups (eg. nice +19 on an autogroup), deeper taskgroup
+ * hierarchies, especially on larger systems. This is not a user-visible change
+ * and does not change the user-interface for setting shares/weights.
+ *
+ * We increase resolution only if we have enough bits to allow this increased
+ * resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution
+ * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
+ * increased costs.
  */
+#if BITS_PER_LONG > 32
+# define SCHED_LOAD_RESOLUTION	10
+# define scale_load(w)		((w) << SCHED_LOAD_RESOLUTION)
+# define scale_load_down(w)	((w) >> SCHED_LOAD_RESOLUTION)
+#else
+# define SCHED_LOAD_RESOLUTION	0
+# define scale_load(w)		(w)
+# define scale_load_down(w)	(w)
+#endif
 
-/*
- * Increase resolution of nice-level calculations:
- */
-#define SCHED_LOAD_SHIFT	10
+#define SCHED_LOAD_SHIFT	(10 + SCHED_LOAD_RESOLUTION)
 #define SCHED_LOAD_SCALE	(1L << SCHED_LOAD_SHIFT)
 
-#define SCHED_LOAD_SCALE_FUZZ	SCHED_LOAD_SCALE
+/*
+ * Increase resolution of cpu_power calculations
+ */
+#define SCHED_POWER_SHIFT	10
+#define SCHED_POWER_SCALE	(1L << SCHED_POWER_SHIFT)
 
+/*
+ * sched-domains (multiprocessor balancing) declarations:
+ */
 #ifdef CONFIG_SMP
 #define SD_LOAD_BALANCE		0x0001	/* Do load balancing on this domain. */
 #define SD_BALANCE_NEWIDLE	0x0002	/* Balance when about to become idle */

index c62acf4..bb504e1 100644
@@ -293,7 +293,7 @@ static DEFINE_SPINLOCK(task_group_lock);
  *  limitation from this.)
  */
 #define MIN_SHARES	2
-#define MAX_SHARES	(1UL << 18)
+#define MAX_SHARES	(1UL << (18 + SCHED_LOAD_RESOLUTION))
 
 static int root_task_group_load = ROOT_TASK_GROUP_LOAD;
 #endif

@@ -1330,13 +1330,25 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
 {
 	u64 tmp;
 
-	tmp = (u64)delta_exec * weight;
+	/*
+	 * weight can be less than 2^SCHED_LOAD_RESOLUTION for task group sched
+	 * entities since MIN_SHARES = 2. Treat weight as 1 if less than
+	 * 2^SCHED_LOAD_RESOLUTION.
+	 */
+	if (likely(weight > (1UL << SCHED_LOAD_RESOLUTION)))
+		tmp = (u64)delta_exec * scale_load_down(weight);
+	else
+		tmp = (u64)delta_exec;
 
 	if (!lw->inv_weight) {
-		if (BITS_PER_LONG > 32 && unlikely(lw->weight >= WMULT_CONST))
+		unsigned long w = scale_load_down(lw->weight);
+
+		if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
 			lw->inv_weight = 1;
+		else if (unlikely(!w))
+			lw->inv_weight = WMULT_CONST;
 		else
-			lw->inv_weight = WMULT_CONST / lw->weight;
+			lw->inv_weight = WMULT_CONST / w;
 	}
 
 	/*

@@ -1778,17 +1790,20 @@ static void dec_nr_running(struct rq *rq)
 
 static void set_load_weight(struct task_struct *p)
 {
+	int prio = p->static_prio - MAX_RT_PRIO;
+	struct load_weight *load = &p->se.load;
+
 	/*
 	 * SCHED_IDLE tasks get minimal weight:
 	 */
 	if (p->policy == SCHED_IDLE) {
-		p->se.load.weight = WEIGHT_IDLEPRIO;
-		p->se.load.inv_weight = WMULT_IDLEPRIO;
+		load->weight = scale_load(WEIGHT_IDLEPRIO);
+		load->inv_weight = WMULT_IDLEPRIO;
 		return;
 	}
 
-	p->se.load.weight = prio_to_weight[p->static_prio - MAX_RT_PRIO];
-	p->se.load.inv_weight = prio_to_wmult[p->static_prio - MAX_RT_PRIO];
+	load->weight = scale_load(prio_to_weight[prio]);
+	load->inv_weight = prio_to_wmult[prio];
 }
 
 static void enqueue_task(struct rq *rq, struct task_struct *p, int flags)

@@ -6527,7 +6542,7 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
 		cpulist_scnprintf(str, sizeof(str), sched_group_cpus(group));
 
 		printk(KERN_CONT " %s", str);
-		if (group->cpu_power != SCHED_LOAD_SCALE) {
+		if (group->cpu_power != SCHED_POWER_SCALE) {
 			printk(KERN_CONT " (cpu_power = %d)",
 				group->cpu_power);
 		}

@@ -7902,7 +7917,7 @@ void __init sched_init(void)
 #ifdef CONFIG_SMP
 		rq->sd = NULL;
 		rq->rd = NULL;
-		rq->cpu_power = SCHED_LOAD_SCALE;
+		rq->cpu_power = SCHED_POWER_SCALE;
 		rq->post_schedule = 0;
 		rq->active_balance = 0;
 		rq->next_balance = jiffies;

@@ -8806,14 +8821,14 @@ cpu_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
 static int cpu_shares_write_u64(struct cgroup *cgrp, struct cftype *cftype,
 				u64 shareval)
 {
-	return sched_group_set_shares(cgroup_tg(cgrp), shareval);
+	return sched_group_set_shares(cgroup_tg(cgrp), scale_load(shareval));
 }
 
 static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)
 {
 	struct task_group *tg = cgroup_tg(cgrp);
 
-	return (u64) tg->shares;
+	return (u64) scale_load_down(tg->shares);
 }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 

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