2 files changed, 41 insertions, 10 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f2f440221b70..c34a718e20dd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -788,9 +788,28 @@ enum cpu_idle_type {
 };
 
 /*
- * Increase resolution of nice-level calculations:
+ * 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.
  */
-#define SCHED_LOAD_SHIFT        10
+#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
+
+#define SCHED_LOAD_SHIFT        (10 + SCHED_LOAD_RESOLUTION)
 #define SCHED_LOAD_SCALE        (1L << SCHED_LOAD_SHIFT)
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index 375e9c677d58..bb504e1839e5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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;
         }
 
         /*
@@ -1785,12 +1797,12 @@ static void set_load_weight(struct task_struct *p)
          * SCHED_IDLE tasks get minimal weight:
          */
         if (p->policy == SCHED_IDLE) {
-                load->weight = WEIGHT_IDLEPRIO;
+                load->weight = scale_load(WEIGHT_IDLEPRIO);
                 load->inv_weight = WMULT_IDLEPRIO;
                 return;
         }
 
-        load->weight = prio_to_weight[prio];
+        load->weight = scale_load(prio_to_weight[prio]);
         load->inv_weight = prio_to_wmult[prio];
 }
 
@@ -8809,14 +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 */