sched: Rewrite tg_shares_up)

By tracking a per-cpu load-avg for each cfs_rq and folding it into a
global task_group load on each tick we can rework tg_shares_up to be
strictly per-cpu.

This should improve cpu-cgroup performance for smp systems
significantly.

[ Paul: changed to use queueing cfs_rq + bug fixes ]

Signed-off-by: Paul Turner <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

Author: Peter Zijlstra

include/linux/sched.h

@@ -1885,8 +1885,6 @@ static inline void wake_up_idle_cpu(int cpu) { }
 extern unsigned int sysctl_sched_latency;
 extern unsigned int sysctl_sched_min_granularity;
 extern unsigned int sysctl_sched_wakeup_granularity;
-extern unsigned int sysctl_sched_shares_ratelimit;
-extern unsigned int sysctl_sched_shares_thresh;
 extern unsigned int sysctl_sched_child_runs_first;
 
 enum sched_tunable_scaling {

kernel/sched.c

@@ -253,6 +253,8 @@ struct task_group {
 	/* runqueue "owned" by this group on each cpu */
 	struct cfs_rq **cfs_rq;
 	unsigned long shares;
+
+	atomic_t load_weight;
 #endif
 
 #ifdef CONFIG_RT_GROUP_SCHED
@@ -359,15 +361,11 @@ struct cfs_rq {
 	 */
 	unsigned long h_load;
 
-	/*
-	 * this cpu's part of tg->shares
-	 */
-	unsigned long shares;
+	u64 load_avg;
+	u64 load_period;
+	u64 load_stamp;
 
-	/*
-	 * load.weight at the time we set shares
-	 */
-	unsigned long rq_weight;
+	unsigned long load_contribution;
 #endif
 #endif
 };
@@ -806,20 +804,6 @@ late_initcall(sched_init_debug);
  */
 const_debug unsigned int sysctl_sched_nr_migrate = 32;
 
-/*
- * ratelimit for updating the group shares.
- * default: 0.25ms
- */
-unsigned int sysctl_sched_shares_ratelimit = 250000;
-unsigned int normalized_sysctl_sched_shares_ratelimit = 250000;
-
-/*
- * Inject some fuzzyness into changing the per-cpu group shares
- * this avoids remote rq-locks at the expense of fairness.
- * default: 4
- */
-unsigned int sysctl_sched_shares_thresh = 4;
-
 /*
  * period over which we average the RT time consumption, measured
  * in ms.
@@ -1369,6 +1353,12 @@ static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
 	lw->inv_weight = 0;
 }
 
+static inline void update_load_set(struct load_weight *lw, unsigned long w)
+{
+	lw->weight = w;
+	lw->inv_weight = 0;
+}
+
 /*
  * To aid in avoiding the subversion of "niceness" due to uneven distribution
  * of tasks with abnormal "nice" values across CPUs the contribution that
@@ -1557,97 +1547,44 @@ static unsigned long cpu_avg_load_per_task(int cpu)
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 
-static __read_mostly unsigned long __percpu *update_shares_data;
-
-static void __set_se_shares(struct sched_entity *se, unsigned long shares);
-
-/*
- * Calculate and set the cpu's group shares.
- */
-static void update_group_shares_cpu(struct task_group *tg, int cpu,
-				    unsigned long sd_shares,
-				    unsigned long sd_rq_weight,
-				    unsigned long *usd_rq_weight)
-{
-	unsigned long shares, rq_weight;
-	int boost = 0;
-
-	rq_weight = usd_rq_weight[cpu];
-	if (!rq_weight) {
-		boost = 1;
-		rq_weight = NICE_0_LOAD;
-	}
-
-	/*
-	 *             \Sum_j shares_j * rq_weight_i
-	 * shares_i =  -----------------------------
-	 *                  \Sum_j rq_weight_j
-	 */
-	shares = (sd_shares * rq_weight) / sd_rq_weight;
-	shares = clamp_t(unsigned long, shares, MIN_SHARES, MAX_SHARES);
-
-	if (abs(shares - tg->se[cpu]->load.weight) >
-			sysctl_sched_shares_thresh) {
-		struct rq *rq = cpu_rq(cpu);
-		unsigned long flags;
-
-		raw_spin_lock_irqsave(&rq->lock, flags);
-		tg->cfs_rq[cpu]->rq_weight = boost ? 0 : rq_weight;
-		tg->cfs_rq[cpu]->shares = boost ? 0 : shares;
-		__set_se_shares(tg->se[cpu], shares);
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
-	}
-}
+static void update_cfs_load(struct cfs_rq *cfs_rq);
+static void update_cfs_shares(struct cfs_rq *cfs_rq);
 
 /*
- * Re-compute the task group their per cpu shares over the given domain.
- * This needs to be done in a bottom-up fashion because the rq weight of a
- * parent group depends on the shares of its child groups.
+ * update tg->load_weight by folding this cpu's load_avg
  */
 static int tg_shares_up(struct task_group *tg, void *data)
 {
-	unsigned long weight, rq_weight = 0, sum_weight = 0, shares = 0;
-	unsigned long *usd_rq_weight;
-	struct sched_domain *sd = data;
+	long load_avg;
+	struct cfs_rq *cfs_rq;
 	unsigned long flags;
-	int i;
+	int cpu = (long)data;
+	struct rq *rq;
 
-	if (!tg->se[0])
+	if (!tg->se[cpu])
 		return 0;
 
-	local_irq_save(flags);
-	usd_rq_weight = per_cpu_ptr(update_shares_data, smp_processor_id());
-
-	for_each_cpu(i, sched_domain_span(sd)) {
-		weight = tg->cfs_rq[i]->load.weight;
-		usd_rq_weight[i] = weight;
-
-		rq_weight += weight;
-		/*
-		 * If there are currently no tasks on the cpu pretend there
-		 * is one of average load so that when a new task gets to
-		 * run here it will not get delayed by group starvation.
-		 */
-		if (!weight)
-			weight = NICE_0_LOAD;
+	rq = cpu_rq(cpu);
+	cfs_rq = tg->cfs_rq[cpu];
 
-		sum_weight += weight;
-		shares += tg->cfs_rq[i]->shares;
-	}
+	raw_spin_lock_irqsave(&rq->lock, flags);
 
-	if (!rq_weight)
-		rq_weight = sum_weight;
+	update_rq_clock(rq);
+	update_cfs_load(cfs_rq);
 
-	if ((!shares && rq_weight) || shares > tg->shares)
-		shares = tg->shares;
+	load_avg = div64_u64(cfs_rq->load_avg, cfs_rq->load_period+1);
+	load_avg -= cfs_rq->load_contribution;
 
-	if (!sd->parent || !(sd->parent->flags & SD_LOAD_BALANCE))
-		shares = tg->shares;
+	atomic_add(load_avg, &tg->load_weight);
+	cfs_rq->load_contribution += load_avg;
 
-	for_each_cpu(i, sched_domain_span(sd))
-		update_group_shares_cpu(tg, i, shares, rq_weight, usd_rq_weight);
+	/*
+	 * We need to update shares after updating tg->load_weight in
+	 * order to adjust the weight of groups with long running tasks.
+	 */
+	update_cfs_shares(cfs_rq);
 
-	local_irq_restore(flags);
+	raw_spin_unlock_irqrestore(&rq->lock, flags);
 
 	return 0;
 }
@@ -1666,7 +1603,7 @@ static int tg_load_down(struct task_group *tg, void *data)
 		load = cpu_rq(cpu)->load.weight;
 	} else {
 		load = tg->parent->cfs_rq[cpu]->h_load;
-		load *= tg->cfs_rq[cpu]->shares;
+		load *= tg->se[cpu]->load.weight;
 		load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
 	}
 
@@ -1675,21 +1612,16 @@ static int tg_load_down(struct task_group *tg, void *data)
 	return 0;
 }
 
-static void update_shares(struct sched_domain *sd)
+static void update_shares(long cpu)
 {
-	s64 elapsed;
-	u64 now;
-
 	if (root_task_group_empty())
 		return;
 
-	now = local_clock();
-	elapsed = now - sd->last_update;
+	/*
+	 * XXX: replace with an on-demand list
+	 */
 
-	if (elapsed >= (s64)(u64)sysctl_sched_shares_ratelimit) {
-		sd->last_update = now;
-		walk_tg_tree(tg_nop, tg_shares_up, sd);
-	}
+	walk_tg_tree(tg_nop, tg_shares_up, (void *)cpu);
 }
 
 static void update_h_load(long cpu)
@@ -1699,7 +1631,7 @@ static void update_h_load(long cpu)
 
 #else
 
-static inline void update_shares(struct sched_domain *sd)
+static inline void update_shares(int cpu)
 {
 }
 
@@ -1824,15 +1756,6 @@ static void double_rq_unlock(struct rq *rq1, struct rq *rq2)
 
 #endif
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-static void cfs_rq_set_shares(struct cfs_rq *cfs_rq, unsigned long shares)
-{
-#ifdef CONFIG_SMP
-	cfs_rq->shares = shares;
-#endif
-}
-#endif
-
 static void calc_load_account_idle(struct rq *this_rq);
 static void update_sysctl(void);
 static int get_update_sysctl_factor(void);
@@ -5551,7 +5474,6 @@ static void update_sysctl(void)
 	SET_SYSCTL(sched_min_granularity);
 	SET_SYSCTL(sched_latency);
 	SET_SYSCTL(sched_wakeup_granularity);
-	SET_SYSCTL(sched_shares_ratelimit);
 #undef SET_SYSCTL
 }
 
@@ -7787,8 +7709,7 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
 		se->cfs_rq = parent->my_q;
 
 	se->my_q = cfs_rq;
-	se->load.weight = tg->shares;
-	se->load.inv_weight = 0;
+	update_load_set(&se->load, tg->shares);
 	se->parent = parent;
 }
 #endif
@@ -7881,10 +7802,6 @@ void __init sched_init(void)
 
 #endif /* CONFIG_CGROUP_SCHED */
 
-#if defined CONFIG_FAIR_GROUP_SCHED && defined CONFIG_SMP
-	update_shares_data = __alloc_percpu(nr_cpu_ids * sizeof(unsigned long),
-					    __alignof__(unsigned long));
-#endif
 	for_each_possible_cpu(i) {
 		struct rq *rq;
 
@@ -8452,8 +8369,7 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares)
 	if (on_rq)
 		dequeue_entity(cfs_rq, se, 0);
 
-	se->load.weight = shares;
-	se->load.inv_weight = 0;
+	update_load_set(&se->load, shares);
 
 	if (on_rq)
 		enqueue_entity(cfs_rq, se, 0);
@@ -8510,7 +8426,6 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
 		/*
 		 * force a rebalance
 		 */
-		cfs_rq_set_shares(tg->cfs_rq[i], 0);
 		set_se_shares(tg->se[i], shares);
 	}
 

kernel/sched_debug.c

@@ -202,15 +202,22 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 	spread0 = min_vruntime - rq0_min_vruntime;
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "spread0",
 			SPLIT_NS(spread0));
-	SEQ_printf(m, "  .%-30s: %ld\n", "nr_running", cfs_rq->nr_running);
-	SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
-
 	SEQ_printf(m, "  .%-30s: %d\n", "nr_spread_over",
 			cfs_rq->nr_spread_over);
+	SEQ_printf(m, "  .%-30s: %ld\n", "nr_running", cfs_rq->nr_running);
+	SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
 #ifdef CONFIG_FAIR_GROUP_SCHED
 #ifdef CONFIG_SMP
-	SEQ_printf(m, "  .%-30s: %lu\n", "shares", cfs_rq->shares);
+	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "load_avg",
+			SPLIT_NS(cfs_rq->load_avg));
+	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "load_period",
+			SPLIT_NS(cfs_rq->load_period));
+	SEQ_printf(m, "  .%-30s: %ld\n", "load_contrib",
+			cfs_rq->load_contribution);
+	SEQ_printf(m, "  .%-30s: %d\n", "load_tg",
+			atomic_read(&tg->load_weight));
 #endif
+
 	print_cfs_group_stats(m, cpu, cfs_rq->tg);
 #endif
 }