net_sched: gen_estimator: complete rewrite of rate estimators

1) Old code was hard to maintain, due to complex lock chains.
   (We probably will be able to remove some kfree_rcu() in callers)

2) Using a single timer to update all estimators does not scale.

3) Code was buggy on 32bit kernel (WRITE_ONCE() on 64bit quantity
   is not supposed to work well)

In this rewrite :

- I removed the RB tree that had to be scanned in
  gen_estimator_active(). qdisc dumps should be much faster.

- Each estimator has its own timer.

- Estimations are maintained in net_rate_estimator structure,
  instead of dirtying the qdisc. Minor, but part of the simplification.

- Reading the estimator uses RCU and a seqcount to provide proper
  support for 32bit kernels.

- We reduce memory need when estimators are not used, since
  we store a pointer, instead of the bytes/packets counters.

- xt_rateest_mt() no longer has to grab a spinlock.
  (In the future, xt_rateest_tg() could be switched to per cpu counters)
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/act_api.h

@@ -36,7 +36,7 @@ struct tc_action {
 	struct tcf_t			tcfa_tm;
 	struct gnet_stats_basic_packed	tcfa_bstats;
 	struct gnet_stats_queue		tcfa_qstats;
-	struct gnet_stats_rate_est64	tcfa_rate_est;
+	struct net_rate_estimator __rcu *tcfa_rate_est;
 	spinlock_t			tcfa_lock;
 	struct rcu_head			tcfa_rcu;
 	struct gnet_stats_basic_cpu __percpu *cpu_bstats;

include/net/gen_stats.h

@@ -11,6 +11,8 @@ struct gnet_stats_basic_cpu {
 	struct u64_stats_sync syncp;
 };
 
+struct net_rate_estimator;
+
 struct gnet_dump {
 	spinlock_t *      lock;
 	struct sk_buff *  skb;
@@ -42,8 +44,7 @@ void __gnet_stats_copy_basic(const seqcount_t *running,
 			     struct gnet_stats_basic_cpu __percpu *cpu,
 			     struct gnet_stats_basic_packed *b);
 int gnet_stats_copy_rate_est(struct gnet_dump *d,
-			     const struct gnet_stats_basic_packed *b,
-			     struct gnet_stats_rate_est64 *r);
+			     struct net_rate_estimator __rcu **ptr);
 int gnet_stats_copy_queue(struct gnet_dump *d,
 			  struct gnet_stats_queue __percpu *cpu_q,
 			  struct gnet_stats_queue *q, __u32 qlen);
@@ -53,16 +54,16 @@ int gnet_stats_finish_copy(struct gnet_dump *d);
 
 int gen_new_estimator(struct gnet_stats_basic_packed *bstats,
 		      struct gnet_stats_basic_cpu __percpu *cpu_bstats,
-		      struct gnet_stats_rate_est64 *rate_est,
+		      struct net_rate_estimator __rcu **rate_est,
 		      spinlock_t *stats_lock,
 		      seqcount_t *running, struct nlattr *opt);
-void gen_kill_estimator(struct gnet_stats_basic_packed *bstats,
-			struct gnet_stats_rate_est64 *rate_est);
+void gen_kill_estimator(struct net_rate_estimator __rcu **ptr);
 int gen_replace_estimator(struct gnet_stats_basic_packed *bstats,
 			  struct gnet_stats_basic_cpu __percpu *cpu_bstats,
-			  struct gnet_stats_rate_est64 *rate_est,
+			  struct net_rate_estimator __rcu **ptr,
 			  spinlock_t *stats_lock,
 			  seqcount_t *running, struct nlattr *opt);
-bool gen_estimator_active(const struct gnet_stats_basic_packed *bstats,
-			  const struct gnet_stats_rate_est64 *rate_est);
+bool gen_estimator_active(struct net_rate_estimator __rcu **ptr);
+bool gen_estimator_read(struct net_rate_estimator __rcu **ptr,
+			struct gnet_stats_rate_est64 *sample);
 #endif

include/net/netfilter/xt_rateest.h

 #ifndef _XT_RATEEST_H
 #define _XT_RATEEST_H
 
+#include <net/gen_stats.h>
+
 struct xt_rateest {
 	/* keep lock and bstats on same cache line to speedup xt_rateest_tg() */
 	struct gnet_stats_basic_packed	bstats;
 	spinlock_t			lock;
-	/* keep rstats and lock on same cache line to speedup xt_rateest_mt() */
-	struct gnet_stats_rate_est64	rstats;
+
 
 	/* following fields not accessed in hot path */
+	unsigned int			refcnt;
 	struct hlist_node		list;
 	char				name[IFNAMSIZ];
-	unsigned int			refcnt;
 	struct gnet_estimator		params;
 	struct rcu_head			rcu;
+
+	/* keep this field far away to speedup xt_rateest_mt() */
+	struct net_rate_estimator __rcu *rate_est;
 };
 
 struct xt_rateest *xt_rateest_lookup(const char *name);

include/net/sch_generic.h

@@ -76,7 +76,7 @@ struct Qdisc {
 
 	struct netdev_queue	*dev_queue;
 
-	struct gnet_stats_rate_est64	rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
 	struct gnet_stats_queue	__percpu *cpu_qstats;
 

net/core/gen_stats.c

@@ -194,8 +194,7 @@ EXPORT_SYMBOL(gnet_stats_copy_basic);
 /**
  * gnet_stats_copy_rate_est - copy rate estimator statistics into statistics TLV
  * @d: dumping handle
- * @b: basic statistics
- * @r: rate estimator statistics
+ * @rate_est: rate estimator
  *
  * Appends the rate estimator statistics to the top level TLV created by
  * gnet_stats_start_copy().
@@ -205,18 +204,17 @@ EXPORT_SYMBOL(gnet_stats_copy_basic);
  */
 int
 gnet_stats_copy_rate_est(struct gnet_dump *d,
-			 const struct gnet_stats_basic_packed *b,
-			 struct gnet_stats_rate_est64 *r)
+			 struct net_rate_estimator __rcu **rate_est)
 {
+	struct gnet_stats_rate_est64 sample;
 	struct gnet_stats_rate_est est;
 	int res;
 
-	if (b && !gen_estimator_active(b, r))
+	if (!gen_estimator_read(rate_est, &sample))
 		return 0;
-
-	est.bps = min_t(u64, UINT_MAX, r->bps);
+	est.bps = min_t(u64, UINT_MAX, sample.bps);
 	/* we have some time before reaching 2^32 packets per second */
-	est.pps = r->pps;
+	est.pps = sample.pps;
 
 	if (d->compat_tc_stats) {
 		d->tc_stats.bps = est.bps;
@@ -226,11 +224,11 @@ gnet_stats_copy_rate_est(struct gnet_dump *d,
 	if (d->tail) {
 		res = gnet_stats_copy(d, TCA_STATS_RATE_EST, &est, sizeof(est),
 				      TCA_STATS_PAD);
-		if (res < 0 || est.bps == r->bps)
+		if (res < 0 || est.bps == sample.bps)
 			return res;
 		/* emit 64bit stats only if needed */
-		return gnet_stats_copy(d, TCA_STATS_RATE_EST64, r, sizeof(*r),
-				       TCA_STATS_PAD);
+		return gnet_stats_copy(d, TCA_STATS_RATE_EST64, &sample,
+				       sizeof(sample), TCA_STATS_PAD);
 	}
 
 	return 0;

net/netfilter/xt_RATEEST.c

@@ -63,7 +63,7 @@ void xt_rateest_put(struct xt_rateest *est)
 	mutex_lock(&xt_rateest_mutex);
 	if (--est->refcnt == 0) {
 		hlist_del(&est->list);
-		gen_kill_estimator(&est->bstats, &est->rstats);
+		gen_kill_estimator(&est->rate_est);
 		/*
 		 * gen_estimator est_timer() might access est->lock or bstats,
 		 * wait a RCU grace period before freeing 'est'
@@ -132,7 +132,7 @@ static int xt_rateest_tg_checkentry(const struct xt_tgchk_param *par)
 	cfg.est.interval	= info->interval;
 	cfg.est.ewma_log	= info->ewma_log;
 
-	ret = gen_new_estimator(&est->bstats, NULL, &est->rstats,
+	ret = gen_new_estimator(&est->bstats, NULL, &est->rate_est,
 				&est->lock, NULL, &cfg.opt);
 	if (ret < 0)
 		goto err2;

net/netfilter/xt_rateest.c

@@ -18,35 +18,33 @@ static bool
 xt_rateest_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	const struct xt_rateest_match_info *info = par->matchinfo;
-	struct gnet_stats_rate_est64 *r;
+	struct gnet_stats_rate_est64 sample = {0};
 	u_int32_t bps1, bps2, pps1, pps2;
 	bool ret = true;
 
-	spin_lock_bh(&info->est1->lock);
-	r = &info->est1->rstats;
+	gen_estimator_read(&info->est1->rate_est, &sample);
+
 	if (info->flags & XT_RATEEST_MATCH_DELTA) {
-		bps1 = info->bps1 >= r->bps ? info->bps1 - r->bps : 0;
-		pps1 = info->pps1 >= r->pps ? info->pps1 - r->pps : 0;
+		bps1 = info->bps1 >= sample.bps ? info->bps1 - sample.bps : 0;
+		pps1 = info->pps1 >= sample.pps ? info->pps1 - sample.pps : 0;
 	} else {
-		bps1 = r->bps;
-		pps1 = r->pps;
+		bps1 = sample.bps;
+		pps1 = sample.pps;
 	}
-	spin_unlock_bh(&info->est1->lock);
 
 	if (info->flags & XT_RATEEST_MATCH_ABS) {
 		bps2 = info->bps2;
 		pps2 = info->pps2;
 	} else {
-		spin_lock_bh(&info->est2->lock);
-		r = &info->est2->rstats;
+		gen_estimator_read(&info->est2->rate_est, &sample);
+
 		if (info->flags & XT_RATEEST_MATCH_DELTA) {
-			bps2 = info->bps2 >= r->bps ? info->bps2 - r->bps : 0;
-			pps2 = info->pps2 >= r->pps ? info->pps2 - r->pps : 0;
+			bps2 = info->bps2 >= sample.bps ? info->bps2 - sample.bps : 0;
+			pps2 = info->pps2 >= sample.pps ? info->pps2 - sample.pps : 0;
 		} else {
-			bps2 = r->bps;
-			pps2 = r->pps;
+			bps2 = sample.bps;
+			pps2 = sample.pps;
 		}
-		spin_unlock_bh(&info->est2->lock);
 	}
 
 	switch (info->mode) {

net/sched/act_api.c

@@ -41,8 +41,7 @@ static void tcf_hash_destroy(struct tcf_hashinfo *hinfo, struct tc_action *p)
 	spin_lock_bh(&hinfo->lock);
 	hlist_del(&p->tcfa_head);
 	spin_unlock_bh(&hinfo->lock);
-	gen_kill_estimator(&p->tcfa_bstats,
-			   &p->tcfa_rate_est);
+	gen_kill_estimator(&p->tcfa_rate_est);
 	/*
 	 * gen_estimator est_timer() might access p->tcfa_lock
 	 * or bstats, wait a RCU grace period before freeing p
@@ -237,8 +236,7 @@ EXPORT_SYMBOL(tcf_hash_check);
 void tcf_hash_cleanup(struct tc_action *a, struct nlattr *est)
 {
 	if (est)
-		gen_kill_estimator(&a->tcfa_bstats,
-				   &a->tcfa_rate_est);
+		gen_kill_estimator(&a->tcfa_rate_est);
 	call_rcu(&a->tcfa_rcu, free_tcf);
 }
 EXPORT_SYMBOL(tcf_hash_cleanup);
@@ -670,8 +668,7 @@ int tcf_action_copy_stats(struct sk_buff *skb, struct tc_action *p,
 		goto errout;
 
 	if (gnet_stats_copy_basic(NULL, &d, p->cpu_bstats, &p->tcfa_bstats) < 0 ||
-	    gnet_stats_copy_rate_est(&d, &p->tcfa_bstats,
-				     &p->tcfa_rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(&d, &p->tcfa_rate_est) < 0 ||
 	    gnet_stats_copy_queue(&d, p->cpu_qstats,
 				  &p->tcfa_qstats,
 				  p->tcfa_qstats.qlen) < 0)

net/sched/act_police.c

@@ -142,8 +142,7 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
 			goto failure_unlock;
 	} else if (tb[TCA_POLICE_AVRATE] &&
 		   (ret == ACT_P_CREATED ||
-		    !gen_estimator_active(&police->tcf_bstats,
-					  &police->tcf_rate_est))) {
+		    !gen_estimator_active(&police->tcf_rate_est))) {
 		err = -EINVAL;
 		goto failure_unlock;
 	}
@@ -216,14 +215,18 @@ static int tcf_act_police(struct sk_buff *skb, const struct tc_action *a,
 	bstats_update(&police->tcf_bstats, skb);
 	tcf_lastuse_update(&police->tcf_tm);
 
-	if (police->tcfp_ewma_rate &&
-	    police->tcf_rate_est.bps >= police->tcfp_ewma_rate) {
+	if (police->tcfp_ewma_rate) {
+		struct gnet_stats_rate_est64 sample;
+
+		if (!gen_estimator_read(&police->tcf_rate_est, &sample) ||
+		    sample.bps >= police->tcfp_ewma_rate) {
 			police->tcf_qstats.overlimits++;
 			if (police->tcf_action == TC_ACT_SHOT)
 				police->tcf_qstats.drops++;
 			spin_unlock(&police->tcf_lock);
 			return police->tcf_action;
 		}
+	}
 
 	if (qdisc_pkt_len(skb) <= police->tcfp_mtu) {
 		if (!police->rate_present) {

net/sched/sch_api.c

@@ -1395,7 +1395,7 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(q),
 				  &d, cpu_bstats, &q->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(&d, &q->bstats, &q->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(&d, &q->rate_est) < 0 ||
 	    gnet_stats_copy_queue(&d, cpu_qstats, &q->qstats, qlen) < 0)
 		goto nla_put_failure;
 

net/sched/sch_cbq.c

@@ -122,7 +122,7 @@ struct cbq_class {
 	psched_time_t		penalized;
 	struct gnet_stats_basic_packed bstats;
 	struct gnet_stats_queue qstats;
-	struct gnet_stats_rate_est64 rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 	struct tc_cbq_xstats	xstats;
 
 	struct tcf_proto __rcu	*filter_list;
@@ -1346,7 +1346,7 @@ cbq_dump_class_stats(struct Qdisc *sch, unsigned long arg,
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
 				  d, NULL, &cl->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
 	    gnet_stats_copy_queue(d, NULL, &cl->qstats, cl->q->q.qlen) < 0)
 		return -1;
 
@@ -1405,7 +1405,7 @@ static void cbq_destroy_class(struct Qdisc *sch, struct cbq_class *cl)
 	tcf_destroy_chain(&cl->filter_list);
 	qdisc_destroy(cl->q);
 	qdisc_put_rtab(cl->R_tab);
-	gen_kill_estimator(&cl->bstats, &cl->rate_est);
+	gen_kill_estimator(&cl->rate_est);
 	if (cl != &q->link)
 		kfree(cl);
 }

net/sched/sch_drr.c

@@ -25,7 +25,7 @@ struct drr_class {
 
 	struct gnet_stats_basic_packed		bstats;
 	struct gnet_stats_queue		qstats;
-	struct gnet_stats_rate_est64	rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 	struct list_head		alist;
 	struct Qdisc			*qdisc;
 
@@ -142,7 +142,7 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 
 static void drr_destroy_class(struct Qdisc *sch, struct drr_class *cl)
 {
-	gen_kill_estimator(&cl->bstats, &cl->rate_est);
+	gen_kill_estimator(&cl->rate_est);
 	qdisc_destroy(cl->qdisc);
 	kfree(cl);
 }
@@ -283,7 +283,7 @@ static int drr_dump_class_stats(struct Qdisc *sch, unsigned long arg,
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
 				  d, NULL, &cl->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
 	    gnet_stats_copy_queue(d, NULL, &cl->qdisc->qstats, qlen) < 0)
 		return -1;
 

net/sched/sch_generic.c

@@ -709,7 +709,7 @@ void qdisc_destroy(struct Qdisc *qdisc)
 
 	qdisc_put_stab(rtnl_dereference(qdisc->stab));
 #endif
-	gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
+	gen_kill_estimator(&qdisc->rate_est);
 	if (ops->reset)
 		ops->reset(qdisc);
 	if (ops->destroy)

net/sched/sch_hfsc.c

@@ -114,7 +114,7 @@ struct hfsc_class {
 
 	struct gnet_stats_basic_packed bstats;
 	struct gnet_stats_queue qstats;
-	struct gnet_stats_rate_est64 rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 	struct tcf_proto __rcu *filter_list; /* filter list */
 	unsigned int	filter_cnt;	/* filter count */
 	unsigned int	level;		/* class level in hierarchy */
@@ -1091,7 +1091,7 @@ hfsc_destroy_class(struct Qdisc *sch, struct hfsc_class *cl)
 
 	tcf_destroy_chain(&cl->filter_list);
 	qdisc_destroy(cl->qdisc);
-	gen_kill_estimator(&cl->bstats, &cl->rate_est);
+	gen_kill_estimator(&cl->rate_est);
 	if (cl != &q->root)
 		kfree(cl);
 }
@@ -1348,7 +1348,7 @@ hfsc_dump_class_stats(struct Qdisc *sch, unsigned long arg,
 	xstats.rtwork  = cl->cl_cumul;
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch), d, NULL, &cl->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
 	    gnet_stats_copy_queue(d, NULL, &cl->qstats, cl->qdisc->q.qlen) < 0)
 		return -1;
 

net/sched/sch_htb.c

@@ -111,7 +111,7 @@ struct htb_class {
 	unsigned int		children;
 	struct htb_class	*parent;	/* parent class */
 
-	struct gnet_stats_rate_est64 rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 
 	/*
 	 * Written often fields
@@ -1145,7 +1145,7 @@ htb_dump_class_stats(struct Qdisc *sch, unsigned long arg, struct gnet_dump *d)
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
 				  d, NULL, &cl->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
 	    gnet_stats_copy_queue(d, NULL, &qs, qlen) < 0)
 		return -1;
 
@@ -1228,7 +1228,7 @@ static void htb_destroy_class(struct Qdisc *sch, struct htb_class *cl)
 		WARN_ON(!cl->un.leaf.q);
 		qdisc_destroy(cl->un.leaf.q);
 	}
-	gen_kill_estimator(&cl->bstats, &cl->rate_est);
+	gen_kill_estimator(&cl->rate_est);
 	tcf_destroy_chain(&cl->filter_list);
 	kfree(cl);
 }

net/sched/sch_qfq.c

@@ -137,7 +137,7 @@ struct qfq_class {
 
 	struct gnet_stats_basic_packed bstats;
 	struct gnet_stats_queue qstats;
-	struct gnet_stats_rate_est64 rate_est;
+	struct net_rate_estimator __rcu *rate_est;
 	struct Qdisc *qdisc;
 	struct list_head alist;		/* Link for active-classes list. */
 	struct qfq_aggregate *agg;	/* Parent aggregate. */
@@ -508,7 +508,7 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 		new_agg = kzalloc(sizeof(*new_agg), GFP_KERNEL);
 		if (new_agg == NULL) {
 			err = -ENOBUFS;
-			gen_kill_estimator(&cl->bstats, &cl->rate_est);
+			gen_kill_estimator(&cl->rate_est);
 			goto destroy_class;
 		}
 		sch_tree_lock(sch);
@@ -533,7 +533,7 @@ static void qfq_destroy_class(struct Qdisc *sch, struct qfq_class *cl)
 	struct qfq_sched *q = qdisc_priv(sch);
 
 	qfq_rm_from_agg(q, cl);
-	gen_kill_estimator(&cl->bstats, &cl->rate_est);
+	gen_kill_estimator(&cl->rate_est);
 	qdisc_destroy(cl->qdisc);
 	kfree(cl);
 }
@@ -667,7 +667,7 @@ static int qfq_dump_class_stats(struct Qdisc *sch, unsigned long arg,
 
 	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
 				  d, NULL, &cl->bstats) < 0 ||
-	    gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
+	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
 	    gnet_stats_copy_queue(d, NULL,
 				  &cl->qdisc->qstats, cl->qdisc->q.qlen) < 0)
 		return -1;