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-rw-r--r--include/linux/sched.h23
-rw-r--r--kernel/sched.c28
2 files changed, 41 insertions, 10 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f2f440221b7..c34a718e20d 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 375e9c677d5..bb504e1839e 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 */