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>

2 files changed, 116 insertions, 203 deletions

diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index 0993844faeea..101b5d0e2142 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -7,6 +7,7 @@
  *		2 of the License, or (at your option) any later version.
  *
  * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
+ *		Eric Dumazet <edumazet@google.com>
  *
  * Changes:
  *              Jamal Hadi Salim - moved it to net/core and reshulfed
@@ -30,171 +31,79 @@
 #include <linux/skbuff.h>
 #include <linux/rtnetlink.h>
 #include <linux/init.h>
-#include <linux/rbtree.h>
 #include <linux/slab.h>
+#include <linux/seqlock.h>
 #include <net/sock.h>
 #include <net/gen_stats.h>
 
-/*
-   This code is NOT intended to be used for statistics collection,
-   its purpose is to provide a base for statistical multiplexing
-   for controlled load service.
-   If you need only statistics, run a user level daemon which
-   periodically reads byte counters.
-
-   Unfortunately, rate estimation is not a very easy task.
-   F.e. I did not find a simple way to estimate the current peak rate
-   and even failed to formulate the problem 8)8)
-
-   So I preferred not to built an estimator into the scheduler,
-   but run this task separately.
-   Ideally, it should be kernel thread(s), but for now it runs
-   from timers, which puts apparent top bounds on the number of rated
-   flows, has minimal overhead on small, but is enough
-   to handle controlled load service, sets of aggregates.
-
-   We measure rate over A=(1<<interval) seconds and evaluate EWMA:
-
-   avrate = avrate*(1-W) + rate*W
-
-   where W is chosen as negative power of 2: W = 2^(-ewma_log)
-
-   The resulting time constant is:
-
-   T = A/(-ln(1-W))
-
-
-   NOTES.
-
-   * avbps and avpps are scaled by 2^5.
-   * both values are reported as 32 bit unsigned values. bps can
-     overflow for fast links : max speed being 34360Mbit/sec
-   * Minimal interval is HZ/4=250msec (it is the greatest common divisor
-     for HZ=100 and HZ=1024 8)), maximal interval
-     is (HZ*2^EST_MAX_INTERVAL)/4 = 8sec. Shorter intervals
-     are too expensive, longer ones can be implemented
-     at user level painlessly.
+/* This code is NOT intended to be used for statistics collection,
+ * its purpose is to provide a base for statistical multiplexing
+ * for controlled load service.
+ * If you need only statistics, run a user level daemon which
+ * periodically reads byte counters.
  */
 
-#define EST_MAX_INTERVAL	5
-
-struct gen_estimator {
-	struct list_head	list;
+struct net_rate_estimator {
 	struct gnet_stats_basic_packed	*bstats;
-	struct gnet_stats_rate_est64	*rate_est;
 	spinlock_t		*stats_lock;
 	seqcount_t		*running;
-	int			ewma_log;
+	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
+	u8			ewma_log;
+	u8			intvl_log; /* period : (250ms << intvl_log) */
+
+	seqcount_t		seq;
 	u32			last_packets;
-	unsigned long		avpps;
 	u64			last_bytes;
+
+	u64			avpps;
 	u64			avbps;
-	struct rcu_head		e_rcu;
-	struct rb_node		node;
-	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
-	struct rcu_head		head;
-};
 
-struct gen_estimator_head {
-	unsigned long		next_jiffies;
-	struct timer_list	timer;
-	struct list_head	list;
+	unsigned long           next_jiffies;
+	struct timer_list       timer;
+	struct rcu_head		rcu;
 };
 
-static struct gen_estimator_head elist[EST_MAX_INTERVAL+1];
-
-/* Protects against NULL dereference */
-static DEFINE_RWLOCK(est_lock);
-
-/* Protects against soft lockup during large deletion */
-static struct rb_root est_root = RB_ROOT;
-static DEFINE_SPINLOCK(est_tree_lock);
-
-static void est_timer(unsigned long arg)
+static void est_fetch_counters(struct net_rate_estimator *e,
+			       struct gnet_stats_basic_packed *b)
 {
-	int idx = (int)arg;
-	struct gen_estimator *e;
+	if (e->stats_lock)
+		spin_lock(e->stats_lock);
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(e, &elist[idx].list, list) {
-		struct gnet_stats_basic_packed b = {0};
-		unsigned long rate;
-		u64 brate;
-
-		if (e->stats_lock)
-			spin_lock(e->stats_lock);
-		read_lock(&est_lock);
-		if (e->bstats == NULL)
-			goto skip;
-
-		__gnet_stats_copy_basic(e->running, &b, e->cpu_bstats, e->bstats);
-
-		brate = (b.bytes - e->last_bytes)<<(7 - idx);
-		e->last_bytes = b.bytes;
-		e->avbps += (brate >> e->ewma_log) - (e->avbps >> e->ewma_log);
-		WRITE_ONCE(e->rate_est->bps, (e->avbps + 0xF) >> 5);
-
-		rate = b.packets - e->last_packets;
-		rate <<= (7 - idx);
-		e->last_packets = b.packets;
-		e->avpps += (rate >> e->ewma_log) - (e->avpps >> e->ewma_log);
-		WRITE_ONCE(e->rate_est->pps, (e->avpps + 0xF) >> 5);
-skip:
-		read_unlock(&est_lock);
-		if (e->stats_lock)
-			spin_unlock(e->stats_lock);
-	}
+	__gnet_stats_copy_basic(e->running, b, e->cpu_bstats, e->bstats);
 
-	if (!list_empty(&elist[idx].list)) {
-		elist[idx].next_jiffies += ((HZ/4) << idx);
+	if (e->stats_lock)
+		spin_unlock(e->stats_lock);
 
-		if (unlikely(time_after_eq(jiffies, elist[idx].next_jiffies))) {
-			/* Ouch... timer was delayed. */
-			elist[idx].next_jiffies = jiffies + 1;
-		}
-		mod_timer(&elist[idx].timer, elist[idx].next_jiffies);
-	}
-	rcu_read_unlock();
 }
 
-static void gen_add_node(struct gen_estimator *est)
+static void est_timer(unsigned long arg)
 {
-	struct rb_node **p = &est_root.rb_node, *parent = NULL;
+	struct net_rate_estimator *est = (struct net_rate_estimator *)arg;
+	struct gnet_stats_basic_packed b;
+	u64 rate, brate;
 
-	while (*p) {
-		struct gen_estimator *e;
+	est_fetch_counters(est, &b);
+	brate = (b.bytes - est->last_bytes) << (8 - est->ewma_log);
+	brate -= (est->avbps >> est->ewma_log);
 
-		parent = *p;
-		e = rb_entry(parent, struct gen_estimator, node);
+	rate = (u64)(b.packets - est->last_packets) << (8 - est->ewma_log);
+	rate -= (est->avpps >> est->ewma_log);
 
-		if (est->bstats > e->bstats)
-			p = &parent->rb_right;
-		else
-			p = &parent->rb_left;
-	}
-	rb_link_node(&est->node, parent, p);
-	rb_insert_color(&est->node, &est_root);
-}
-
-static
-struct gen_estimator *gen_find_node(const struct gnet_stats_basic_packed *bstats,
-				    const struct gnet_stats_rate_est64 *rate_est)
-{
-	struct rb_node *p = est_root.rb_node;
+	write_seqcount_begin(&est->seq);
+	est->avbps += brate;
+	est->avpps += rate;
+	write_seqcount_end(&est->seq);
 
-	while (p) {
-		struct gen_estimator *e;
+	est->last_bytes = b.bytes;
+	est->last_packets = b.packets;
 
-		e = rb_entry(p, struct gen_estimator, node);
+	est->next_jiffies += ((HZ/4) << est->intvl_log);
 
-		if (bstats > e->bstats)
-			p = p->rb_right;
-		else if (bstats < e->bstats || rate_est != e->rate_est)
-			p = p->rb_left;
-		else
-			return e;
+	if (unlikely(time_after_eq(jiffies, est->next_jiffies))) {
+		/* Ouch... timer was delayed. */
+		est->next_jiffies = jiffies + 1;
 	}
-	return NULL;
+	mod_timer(&est->timer, est->next_jiffies);
 }
 
 /**
@@ -217,84 +126,76 @@ struct gen_estimator *gen_find_node(const struct gnet_stats_basic_packed *bstats
  */
 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)
 {
-	struct gen_estimator *est;
 	struct gnet_estimator *parm = nla_data(opt);
-	struct gnet_stats_basic_packed b = {0};
-	int idx;
+	struct net_rate_estimator *old, *est;
+	struct gnet_stats_basic_packed b;
+	int intvl_log;
 
 	if (nla_len(opt) < sizeof(*parm))
 		return -EINVAL;
 
+	/* allowed timer periods are :
+	 * -2 : 250ms,   -1 : 500ms,    0 : 1 sec
+	 *  1 : 2 sec,    2 : 4 sec,    3 : 8 sec
+	 */
 	if (parm->interval < -2 || parm->interval > 3)
 		return -EINVAL;
 
 	est = kzalloc(sizeof(*est), GFP_KERNEL);
-	if (est == NULL)
+	if (!est)
 		return -ENOBUFS;
 
-	__gnet_stats_copy_basic(running, &b, cpu_bstats, bstats);
-
-	idx = parm->interval + 2;
+	seqcount_init(&est->seq);
+	intvl_log = parm->interval + 2;
 	est->bstats = bstats;
-	est->rate_est = rate_est;
 	est->stats_lock = stats_lock;
 	est->running  = running;
 	est->ewma_log = parm->ewma_log;
-	est->last_bytes = b.bytes;
-	est->avbps = rate_est->bps<<5;
-	est->last_packets = b.packets;
-	est->avpps = rate_est->pps<<10;
+	est->intvl_log = intvl_log;
 	est->cpu_bstats = cpu_bstats;
 
-	spin_lock_bh(&est_tree_lock);
-	if (!elist[idx].timer.function) {
-		INIT_LIST_HEAD(&elist[idx].list);
-		setup_timer(&elist[idx].timer, est_timer, idx);
+	est_fetch_counters(est, &b);
+	est->last_bytes = b.bytes;
+	est->last_packets = b.packets;
+	old = rcu_dereference_protected(*rate_est, 1);
+	if (old) {
+		del_timer_sync(&old->timer);
+		est->avbps = old->avbps;
+		est->avpps = old->avpps;
 	}
 
-	if (list_empty(&elist[idx].list)) {
-		elist[idx].next_jiffies = jiffies + ((HZ/4) << idx);
-		mod_timer(&elist[idx].timer, elist[idx].next_jiffies);
-	}
-	list_add_rcu(&est->list, &elist[idx].list);
-	gen_add_node(est);
-	spin_unlock_bh(&est_tree_lock);
+	est->next_jiffies = jiffies + ((HZ/4) << intvl_log);
+	setup_timer(&est->timer, est_timer, (unsigned long)est);
+	mod_timer(&est->timer, est->next_jiffies);
 
+	rcu_assign_pointer(*rate_est, est);
+	if (old)
+		kfree_rcu(old, rcu);
 	return 0;
 }
 EXPORT_SYMBOL(gen_new_estimator);
 
 /**
  * gen_kill_estimator - remove a rate estimator
- * @bstats: basic statistics
- * @rate_est: rate estimator statistics
+ * @rate_est: rate estimator
  *
- * Removes the rate estimator specified by &bstats and &rate_est.
+ * Removes the rate estimator.
  *
- * Note : Caller should respect an RCU grace period before freeing stats_lock
  */
-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 **rate_est)
 {
-	struct gen_estimator *e;
-
-	spin_lock_bh(&est_tree_lock);
-	while ((e = gen_find_node(bstats, rate_est))) {
-		rb_erase(&e->node, &est_root);
+	struct net_rate_estimator *est;
 
-		write_lock(&est_lock);
-		e->bstats = NULL;
-		write_unlock(&est_lock);
-
-		list_del_rcu(&e->list);
-		kfree_rcu(e, e_rcu);
+	est = xchg((__force struct net_rate_estimator **)rate_est, NULL);
+	if (est) {
+		del_timer_sync(&est->timer);
+		kfree_rcu(est, rcu);
 	}
-	spin_unlock_bh(&est_tree_lock);
 }
 EXPORT_SYMBOL(gen_kill_estimator);
 
@@ -314,33 +215,47 @@ EXPORT_SYMBOL(gen_kill_estimator);
  */
 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 **rate_est,
 			  spinlock_t *stats_lock,
 			  seqcount_t *running, struct nlattr *opt)
 {
-	gen_kill_estimator(bstats, rate_est);
-	return gen_new_estimator(bstats, cpu_bstats, rate_est, stats_lock, running, opt);
+	return gen_new_estimator(bstats, cpu_bstats, rate_est,
+				 stats_lock, running, opt);
 }
 EXPORT_SYMBOL(gen_replace_estimator);
 
 /**
  * gen_estimator_active - test if estimator is currently in use
- * @bstats: basic statistics
- * @rate_est: rate estimator statistics
+ * @rate_est: rate estimator
  *
  * Returns true if estimator is active, and false if not.
  */
-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 **rate_est)
 {
-	bool res;
+	return !!rcu_access_pointer(*rate_est);
+}
+EXPORT_SYMBOL(gen_estimator_active);
 
-	ASSERT_RTNL();
+bool gen_estimator_read(struct net_rate_estimator __rcu **rate_est,
+			struct gnet_stats_rate_est64 *sample)
+{
+	struct net_rate_estimator *est;
+	unsigned seq;
+
+	rcu_read_lock();
+	est = rcu_dereference(*rate_est);
+	if (!est) {
+		rcu_read_unlock();
+		return false;
+	}
 
-	spin_lock_bh(&est_tree_lock);
-	res = gen_find_node(bstats, rate_est) != NULL;
-	spin_unlock_bh(&est_tree_lock);
+	do {
+		seq = read_seqcount_begin(&est->seq);
+		sample->bps = est->avbps >> 8;
+		sample->pps = est->avpps >> 8;
+	} while (read_seqcount_retry(&est->seq, seq));
 
-	return res;
+	rcu_read_unlock();
+	return true;
 }
-EXPORT_SYMBOL(gen_estimator_active);
+EXPORT_SYMBOL(gen_estimator_read);
diff --git a/net/core/gen_stats.c b/net/core/gen_stats.c
index 508e051304fb..87f28557b329 100644
--- a/net/core/gen_stats.c
+++ b/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;