[RFC][PATCH 1/3] sched: Rewrite tg_shares_up

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: sched-rework-tg_shares_up.patch --]
[-- Type: text/plain, Size: 18700 bytes --]

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.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/sched.h   |    2 
 kernel/sched.c          |  173 ++++++++++++------------------------------------
 kernel/sched_debug.c    |   11 ++-
 kernel/sched_fair.c     |  153 ++++++++++++++++++++++++++----------------
 kernel/sched_features.h |    2 
 kernel/sysctl.c         |   17 ----
 6 files changed, 147 insertions(+), 211 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1858,8 +1858,6 @@ static inline void wake_up_idle_cpu(int 
 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 {
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/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
 };
@@ -793,20 +791,6 @@ 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.
  *
@@ -1351,6 +1335,12 @@ static inline void update_load_sub(struc
 	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
@@ -1539,97 +1529,44 @@ static unsigned long cpu_avg_load_per_ta
 
 #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;
+	unsigned 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;
 }
@@ -1648,7 +1585,7 @@ static int tg_load_down(struct task_grou
 		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;
 	}
 
@@ -1657,21 +1594,16 @@ static int tg_load_down(struct task_grou
 	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)
@@ -1681,7 +1613,7 @@ static void update_h_load(long cpu)
 
 #else
 
-static inline void update_shares(struct sched_domain *sd)
+static inline void update_shares(int cpu)
 {
 }
 
@@ -1806,15 +1738,6 @@ static void double_rq_unlock(struct rq *
 
 #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);
@@ -5400,7 +5323,6 @@ 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
 }
 
@@ -7652,8 +7574,7 @@ static void init_tg_cfs_entry(struct tas
 		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
@@ -7746,10 +7667,6 @@ 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;
 
@@ -8317,8 +8234,7 @@ static void __set_se_shares(struct sched
 	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);
@@ -8375,7 +8291,6 @@ int sched_group_set_shares(struct task_g
 		/*
 		 * force a rebalance
 		 */
-		cfs_rq_set_shares(tg->cfs_rq[i], 0);
 		set_se_shares(tg->se[i], shares);
 	}
 
Index: linux-2.6/kernel/sched_debug.c
===================================================================
--- linux-2.6.orig/kernel/sched_debug.c
+++ linux-2.6/kernel/sched_debug.c
@@ -204,13 +204,18 @@ void print_cfs_rq(struct seq_file *m, in
 			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: %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));
 
 	SEQ_printf(m, "  .%-30s: %d\n", "nr_spread_over",
 			cfs_rq->nr_spread_over);
 #ifdef CONFIG_FAIR_GROUP_SCHED
-#ifdef CONFIG_SMP
-	SEQ_printf(m, "  .%-30s: %lu\n", "shares", cfs_rq->shares);
-#endif
 	print_cfs_group_stats(m, cpu, cfs_rq->tg);
 #endif
 }
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -417,7 +417,6 @@ int sched_proc_update_handler(struct ctl
 	WRT_SYSCTL(sched_min_granularity);
 	WRT_SYSCTL(sched_latency);
 	WRT_SYSCTL(sched_wakeup_granularity);
-	WRT_SYSCTL(sched_shares_ratelimit);
 #undef WRT_SYSCTL
 
 	return 0;
@@ -633,7 +632,6 @@ account_entity_enqueue(struct cfs_rq *cf
 		list_add(&se->group_node, &cfs_rq->tasks);
 	}
 	cfs_rq->nr_running++;
-	se->on_rq = 1;
 }
 
 static void
@@ -647,9 +645,84 @@ account_entity_dequeue(struct cfs_rq *cf
 		list_del_init(&se->group_node);
 	}
 	cfs_rq->nr_running--;
-	se->on_rq = 0;
 }
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static void update_cfs_load(struct cfs_rq *cfs_rq)
+{
+	u64 period = sched_avg_period();
+	u64 now = rq_of(cfs_rq)->clock;
+	u64 delta = now - cfs_rq->load_stamp;
+
+	cfs_rq->load_stamp = now;
+	cfs_rq->load_period += delta;
+	cfs_rq->load_avg += delta * cfs_rq->load.weight;
+
+	while (cfs_rq->load_period > period) {
+		/*
+		 * Inline assembly required to prevent the compiler
+		 * optimising this loop into a divmod call.
+		 * See __iter_div_u64_rem() for another example of this.
+		 */
+		asm("" : "+rm" (cfs_rq->load_period));
+		cfs_rq->load_period /= 2;
+		cfs_rq->load_avg /= 2;
+	}
+}
+
+static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
+			    unsigned long weight)
+{
+	if (se->on_rq)
+		account_entity_dequeue(cfs_rq, se);
+
+	update_load_set(&se->load, weight);
+
+	if (se->on_rq)
+		account_entity_enqueue(cfs_rq, se);
+}
+
+static void update_cfs_shares(struct cfs_rq *cfs_rq)
+{
+	struct task_group *tg;
+	struct sched_entity *se;
+	unsigned long load_weight, load, shares;
+
+	if (!cfs_rq)
+		return;
+
+	tg = cfs_rq->tg;
+	se = tg->se[cpu_of(rq_of(cfs_rq))];
+	if (!se)
+		return;
+
+	load = cfs_rq->load.weight;
+
+	load_weight = atomic_read(&tg->load_weight);
+	load_weight -= cfs_rq->load_contribution;
+	load_weight += load;
+
+	shares = (tg->shares * load);
+	if (load_weight)
+		shares /= load_weight;
+
+	if (shares < MIN_SHARES)
+		shares = MIN_SHARES;
+	if (shares > tg->shares)
+		shares = tg->shares;
+
+	reweight_entity(cfs_rq_of(se), se, shares);
+}
+#else /* CONFIG_FAIR_GROUP_SCHED */
+static inline void update_cfs_load(struct cfs_rq *cfs_rq)
+{
+}
+
+static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
+{
+}
+#endif /* CONFIG_FAIR_GROUP_SCHED */
+
 static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 #ifdef CONFIG_SCHEDSTATS
@@ -771,7 +844,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 	 * Update run-time statistics of the 'current'.
 	 */
 	update_curr(cfs_rq);
+	update_cfs_load(cfs_rq);
 	account_entity_enqueue(cfs_rq, se);
+	update_cfs_shares(group_cfs_rq(se));
 
 	if (flags & ENQUEUE_WAKEUP) {
 		place_entity(cfs_rq, se, 0);
@@ -782,6 +857,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 	check_spread(cfs_rq, se);
 	if (se != cfs_rq->curr)
 		__enqueue_entity(cfs_rq, se);
+	se->on_rq = 1;
 }
 
 static void __clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -825,8 +901,11 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
 
 	if (se != cfs_rq->curr)
 		__dequeue_entity(cfs_rq, se);
+	se->on_rq = 0;
+	update_cfs_load(cfs_rq);
 	account_entity_dequeue(cfs_rq, se);
 	update_min_vruntime(cfs_rq);
+	update_cfs_shares(group_cfs_rq(se));
 
 	/*
 	 * Normalize the entity after updating the min_vruntime because the
@@ -1055,6 +1134,9 @@ enqueue_task_fair(struct rq *rq, struct 
 		flags = ENQUEUE_WAKEUP;
 	}
 
+	for_each_sched_entity(se)
+		update_cfs_shares(group_cfs_rq(se));
+
 	hrtick_update(rq);
 }
 
@@ -1071,12 +1153,16 @@ static void dequeue_task_fair(struct rq 
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
 		dequeue_entity(cfs_rq, se, flags);
+
 		/* Don't dequeue parent if it has other entities besides us */
 		if (cfs_rq->load.weight)
 			break;
 		flags |= DEQUEUE_SLEEP;
 	}
 
+	for_each_sched_entity(se)
+		update_cfs_shares(group_cfs_rq(se));
+
 	hrtick_update(rq);
 }
 
@@ -1143,51 +1229,20 @@ static void task_waking_fair(struct rq *
  * 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.
- *
- * The problem is that perfectly aligning the shares is rather expensive, hence
- * we try to avoid doing that too often - see update_shares(), which ratelimits
- * this change.
- *
- * We compensate this by not only taking the current delta into account, but
- * also considering the delta between when the shares were last adjusted and
- * now.
- *
- * We still saw a performance dip, some tracing learned us that between
- * cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased
- * significantly. Therefore try to bias the error in direction of failing
- * the affine wakeup.
- *
  */
-static long effective_load(struct task_group *tg, int cpu,
-		long wl, long wg)
+static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 {
 	struct sched_entity *se = tg->se[cpu];
 
 	if (!tg->parent)
 		return wl;
 
-	/*
-	 * By not taking the decrease of shares on the other cpu into
-	 * account our error leans towards reducing the affine wakeups.
-	 */
-	if (!wl && sched_feat(ASYM_EFF_LOAD))
-		return wl;
-
 	for_each_sched_entity(se) {
 		long S, rw, s, a, b;
-		long more_w;
 
-		/*
-		 * Instead of using this increment, also add the difference
-		 * between when the shares were last updated and now.
-		 */
-		more_w = se->my_q->load.weight - se->my_q->rq_weight;
-		wl += more_w;
-		wg += more_w;
-
-		S = se->my_q->tg->shares;
-		s = se->my_q->shares;
-		rw = se->my_q->rq_weight;
+		S = tg->shares;
+		s = se->load.weight;
+		rw = se->my_q->load.weight;
 
 		a = S*(rw + wl);
 		b = S*rw + s*wg;
@@ -1509,23 +1564,6 @@ select_task_rq_fair(struct rq *rq, struc
 			sd = tmp;
 	}
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	if (sched_feat(LB_SHARES_UPDATE)) {
-		/*
-		 * Pick the largest domain to update shares over
-		 */
-		tmp = sd;
-		if (affine_sd && (!tmp || affine_sd->span_weight > sd->span_weight))
-			tmp = affine_sd;
-
-		if (tmp) {
-			raw_spin_unlock(&rq->lock);
-			update_shares(tmp);
-			raw_spin_lock(&rq->lock);
-		}
-	}
-#endif
-
 	if (affine_sd) {
 		if (cpu == prev_cpu || wake_affine(affine_sd, p, sync))
 			return select_idle_sibling(p, cpu);
@@ -2980,7 +3018,6 @@ static int load_balance(int this_cpu, st
 	schedstat_inc(sd, lb_count[idle]);
 
 redo:
-	update_shares(sd);
 	group = find_busiest_group(sd, this_cpu, &imbalance, idle, &sd_idle,
 				   cpus, balance);
 
@@ -3115,8 +3152,6 @@ out_one_pinned:
 	else
 		ld_moved = 0;
 out:
-	if (ld_moved)
-		update_shares(sd);
 	return ld_moved;
 }
 
@@ -3510,6 +3545,8 @@ static void rebalance_domains(int cpu, e
 	int update_next_balance = 0;
 	int need_serialize;
 
+	update_shares(cpu);
+
 	for_each_domain(cpu, sd) {
 		if (!(sd->flags & SD_LOAD_BALANCE))
 			continue;
Index: linux-2.6/kernel/sched_features.h
===================================================================
--- linux-2.6.orig/kernel/sched_features.h
+++ linux-2.6/kernel/sched_features.h
@@ -52,8 +52,6 @@ SCHED_FEAT(ARCH_POWER, 0)
 SCHED_FEAT(HRTICK, 0)
 SCHED_FEAT(DOUBLE_TICK, 0)
 SCHED_FEAT(LB_BIAS, 1)
-SCHED_FEAT(LB_SHARES_UPDATE, 1)
-SCHED_FEAT(ASYM_EFF_LOAD, 1)
 
 /*
  * Spin-wait on mutex acquisition when the mutex owner is running on
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -307,15 +307,6 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &max_wakeup_granularity_ns,
 	},
 	{
-		.procname	= "sched_shares_ratelimit",
-		.data		= &sysctl_sched_shares_ratelimit,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= sched_proc_update_handler,
-		.extra1		= &min_sched_shares_ratelimit,
-		.extra2		= &max_sched_shares_ratelimit,
-	},
-	{
 		.procname	= "sched_tunable_scaling",
 		.data		= &sysctl_sched_tunable_scaling,
 		.maxlen		= sizeof(enum sched_tunable_scaling),
@@ -325,14 +316,6 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &max_sched_tunable_scaling,
 	},
 	{
-		.procname	= "sched_shares_thresh",
-		.data		= &sysctl_sched_shares_thresh,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
-	},
-	{
 		.procname	= "sched_migration_cost",
 		.data		= &sysctl_sched_migration_cost,
 		.maxlen		= sizeof(unsigned int),