/* net/sched/sch_hhf.c		Heavy-Hitter Filter (HHF)
   *
   * Copyright (C) 2013 Terry Lam <vtlam@google.com>
   * Copyright (C) 2013 Nandita Dukkipati <nanditad@google.com>
   */
  
  #include <linux/jhash.h>
  #include <linux/jiffies.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/vmalloc.h>
  #include <net/flow_keys.h>
  #include <net/pkt_sched.h>
  #include <net/sock.h>
  
  /*	Heavy-Hitter Filter (HHF)
   *
   * Principles :
   * Flows are classified into two buckets: non-heavy-hitter and heavy-hitter
   * buckets. Initially, a new flow starts as non-heavy-hitter. Once classified
   * as heavy-hitter, it is immediately switched to the heavy-hitter bucket.
   * The buckets are dequeued by a Weighted Deficit Round Robin (WDRR) scheduler,
   * in which the heavy-hitter bucket is served with less weight.
   * In other words, non-heavy-hitters (e.g., short bursts of critical traffic)
   * are isolated from heavy-hitters (e.g., persistent bulk traffic) and also have
   * higher share of bandwidth.
   *
   * To capture heavy-hitters, we use the "multi-stage filter" algorithm in the
   * following paper:
   * [EV02] C. Estan and G. Varghese, "New Directions in Traffic Measurement and
   * Accounting", in ACM SIGCOMM, 2002.
   *
   * Conceptually, a multi-stage filter comprises k independent hash functions
   * and k counter arrays. Packets are indexed into k counter arrays by k hash
   * functions, respectively. The counters are then increased by the packet sizes.
   * Therefore,
   *    - For a heavy-hitter flow: *all* of its k array counters must be large.
   *    - For a non-heavy-hitter flow: some of its k array counters can be large
   *      due to hash collision with other small flows; however, with high
   *      probability, not *all* k counters are large.
   *
   * By the design of the multi-stage filter algorithm, the false negative rate
   * (heavy-hitters getting away uncaptured) is zero. However, the algorithm is
   * susceptible to false positives (non-heavy-hitters mistakenly classified as
   * heavy-hitters).
   * Therefore, we also implement the following optimizations to reduce false
   * positives by avoiding unnecessary increment of the counter values:
   *    - Optimization O1: once a heavy-hitter is identified, its bytes are not
   *        accounted in the array counters. This technique is called "shielding"
   *        in Section 3.3.1 of [EV02].
   *    - Optimization O2: conservative update of counters
   *                       (Section 3.3.2 of [EV02]),
   *        New counter value = max {old counter value,
   *                                 smallest counter value + packet bytes}
   *
   * Finally, we refresh the counters periodically since otherwise the counter
   * values will keep accumulating.
   *
   * Once a flow is classified as heavy-hitter, we also save its per-flow state
   * in an exact-matching flow table so that its subsequent packets can be
   * dispatched to the heavy-hitter bucket accordingly.
   *
   *
   * At a high level, this qdisc works as follows:
   * Given a packet p:
   *   - If the flow-id of p (e.g., TCP 5-tuple) is already in the exact-matching
   *     heavy-hitter flow table, denoted table T, then send p to the heavy-hitter
   *     bucket.
   *   - Otherwise, forward p to the multi-stage filter, denoted filter F
   *        + If F decides that p belongs to a non-heavy-hitter flow, then send p
   *          to the non-heavy-hitter bucket.
   *        + Otherwise, if F decides that p belongs to a new heavy-hitter flow,
   *          then set up a new flow entry for the flow-id of p in the table T and
   *          send p to the heavy-hitter bucket.
   *
   * In this implementation:
   *   - T is a fixed-size hash-table with 1024 entries. Hash collision is
   *     resolved by linked-list chaining.
   *   - F has four counter arrays, each array containing 1024 32-bit counters.
   *     That means 4 * 1024 * 32 bits = 16KB of memory.
   *   - Since each array in F contains 1024 counters, 10 bits are sufficient to
   *     index into each array.
   *     Hence, instead of having four hash functions, we chop the 32-bit
   *     skb-hash into three 10-bit chunks, and the remaining 10-bit chunk is
   *     computed as XOR sum of those three chunks.
   *   - We need to clear the counter arrays periodically; however, directly
   *     memsetting 16KB of memory can lead to cache eviction and unwanted delay.
   *     So by representing each counter by a valid bit, we only need to reset
   *     4K of 1 bit (i.e. 512 bytes) instead of 16KB of memory.
   *   - The Deficit Round Robin engine is taken from fq_codel implementation
   *     (net/sched/sch_fq_codel.c). Note that wdrr_bucket corresponds to
   *     fq_codel_flow in fq_codel implementation.
   *
   */
  
  /* Non-configurable parameters */
  #define HH_FLOWS_CNT	 1024  /* number of entries in exact-matching table T */
  #define HHF_ARRAYS_CNT	 4     /* number of arrays in multi-stage filter F */
  #define HHF_ARRAYS_LEN	 1024  /* number of counters in each array of F */
  #define HHF_BIT_MASK_LEN 10    /* masking 10 bits */
  #define HHF_BIT_MASK	 0x3FF /* bitmask of 10 bits */
  
  #define WDRR_BUCKET_CNT  2     /* two buckets for Weighted DRR */
  enum wdrr_bucket_idx {
  	WDRR_BUCKET_FOR_HH	= 0, /* bucket id for heavy-hitters */
  	WDRR_BUCKET_FOR_NON_HH	= 1  /* bucket id for non-heavy-hitters */
  };
  
  #define hhf_time_before(a, b)	\
  	(typecheck(u32, a) && typecheck(u32, b) && ((s32)((a) - (b)) < 0))
  
  /* Heavy-hitter per-flow state */
  struct hh_flow_state {
  	u32		 hash_id;	/* hash of flow-id (e.g. TCP 5-tuple) */
  	u32		 hit_timestamp;	/* last time heavy-hitter was seen */
  	struct list_head flowchain;	/* chaining under hash collision */
  };
  
  /* Weighted Deficit Round Robin (WDRR) scheduler */
  struct wdrr_bucket {
  	struct sk_buff	  *head;
  	struct sk_buff	  *tail;
  	struct list_head  bucketchain;
  	int		  deficit;
  };
  
  struct hhf_sched_data {
  	struct wdrr_bucket buckets[WDRR_BUCKET_CNT];
  	u32		   perturbation;   /* hash perturbation */
  	u32		   quantum;        /* psched_mtu(qdisc_dev(sch)); */
  	u32		   drop_overlimit; /* number of times max qdisc packet
  					    * limit was hit
  					    */
  	struct list_head   *hh_flows;       /* table T (currently active HHs) */
  	u32		   hh_flows_limit;            /* max active HH allocs */
  	u32		   hh_flows_overlimit; /* num of disallowed HH allocs */
  	u32		   hh_flows_total_cnt;          /* total admitted HHs */
  	u32		   hh_flows_current_cnt;        /* total current HHs  */
  	u32		   *hhf_arrays[HHF_ARRAYS_CNT]; /* HH filter F */
  	u32		   hhf_arrays_reset_timestamp;  /* last time hhf_arrays
  							 * was reset
  							 */
  	unsigned long	   *hhf_valid_bits[HHF_ARRAYS_CNT]; /* shadow valid bits
  							     * of hhf_arrays
  							     */
  	/* Similar to the "new_flows" vs. "old_flows" concept in fq_codel DRR */
  	struct list_head   new_buckets; /* list of new buckets */
  	struct list_head   old_buckets; /* list of old buckets */
  
  	/* Configurable HHF parameters */
  	u32		   hhf_reset_timeout; /* interval to reset counter
  					       * arrays in filter F
  					       * (default 40ms)
  					       */
  	u32		   hhf_admit_bytes;   /* counter thresh to classify as
  					       * HH (default 128KB).
  					       * With these default values,
  					       * 128KB / 40ms = 25 Mbps
  					       * i.e., we expect to capture HHs
  					       * sending > 25 Mbps.
  					       */
  	u32		   hhf_evict_timeout; /* aging threshold to evict idle
  					       * HHs out of table T. This should
  					       * be large enough to avoid
  					       * reordering during HH eviction.
  					       * (default 1s)
  					       */
  	u32		   hhf_non_hh_weight; /* WDRR weight for non-HHs
  					       * (default 2,
  					       *  i.e., non-HH : HH = 2 : 1)
  					       */
  };
  
  static u32 hhf_time_stamp(void)
  {
  	return jiffies;
  }
  
  static unsigned int skb_hash(const struct hhf_sched_data *q,
  			     const struct sk_buff *skb)
  {
  	struct flow_keys keys;
  	unsigned int hash;
  
  	if (skb->sk && skb->sk->sk_hash)
  		return skb->sk->sk_hash;
  
  	skb_flow_dissect(skb, &keys);
  	hash = jhash_3words((__force u32)keys.dst,
  			    (__force u32)keys.src ^ keys.ip_proto,
  			    (__force u32)keys.ports, q->perturbation);
  	return hash;
  }
  
  /* Looks up a heavy-hitter flow in a chaining list of table T. */
  static struct hh_flow_state *seek_list(const u32 hash,
  				       struct list_head *head,
  				       struct hhf_sched_data *q)
  {
  	struct hh_flow_state *flow, *next;
  	u32 now = hhf_time_stamp();
  
  	if (list_empty(head))
  		return NULL;
  
  	list_for_each_entry_safe(flow, next, head, flowchain) {
  		u32 prev = flow->hit_timestamp + q->hhf_evict_timeout;
  
  		if (hhf_time_before(prev, now)) {
  			/* Delete expired heavy-hitters, but preserve one entry
  			 * to avoid kzalloc() when next time this slot is hit.
  			 */
  			if (list_is_last(&flow->flowchain, head))
  				return NULL;
  			list_del(&flow->flowchain);
  			kfree(flow);
  			q->hh_flows_current_cnt--;
  		} else if (flow->hash_id == hash) {
  			return flow;
  		}
  	}
  	return NULL;
  }
  
  /* Returns a flow state entry for a new heavy-hitter.  Either reuses an expired
   * entry or dynamically alloc a new entry.
   */
  static struct hh_flow_state *alloc_new_hh(struct list_head *head,
  					  struct hhf_sched_data *q)
  {
  	struct hh_flow_state *flow;
  	u32 now = hhf_time_stamp();
  
  	if (!list_empty(head)) {
  		/* Find an expired heavy-hitter flow entry. */
  		list_for_each_entry(flow, head, flowchain) {
  			u32 prev = flow->hit_timestamp + q->hhf_evict_timeout;
  
  			if (hhf_time_before(prev, now))
  				return flow;
  		}
  	}
  
  	if (q->hh_flows_current_cnt >= q->hh_flows_limit) {
  		q->hh_flows_overlimit++;
  		return NULL;
  	}
  	/* Create new entry. */
  	flow = kzalloc(sizeof(struct hh_flow_state), GFP_ATOMIC);
  	if (!flow)
  		return NULL;
  
  	q->hh_flows_current_cnt++;
  	INIT_LIST_HEAD(&flow->flowchain);
  	list_add_tail(&flow->flowchain, head);
  
  	return flow;
  }
  
  /* Assigns packets to WDRR buckets.  Implements a multi-stage filter to
   * classify heavy-hitters.
   */
  static enum wdrr_bucket_idx hhf_classify(struct sk_buff *skb, struct Qdisc *sch)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	u32 tmp_hash, hash;
  	u32 xorsum, filter_pos[HHF_ARRAYS_CNT], flow_pos;
  	struct hh_flow_state *flow;
  	u32 pkt_len, min_hhf_val;
  	int i;
  	u32 prev;
  	u32 now = hhf_time_stamp();
  
  	/* Reset the HHF counter arrays if this is the right time. */
  	prev = q->hhf_arrays_reset_timestamp + q->hhf_reset_timeout;
  	if (hhf_time_before(prev, now)) {
  		for (i = 0; i < HHF_ARRAYS_CNT; i++)
  			bitmap_zero(q->hhf_valid_bits[i], HHF_ARRAYS_LEN);
  		q->hhf_arrays_reset_timestamp = now;
  	}
  
  	/* Get hashed flow-id of the skb. */
  	hash = skb_hash(q, skb);
  
  	/* Check if this packet belongs to an already established HH flow. */
  	flow_pos = hash & HHF_BIT_MASK;
  	flow = seek_list(hash, &q->hh_flows[flow_pos], q);
  	if (flow) { /* found its HH flow */
  		flow->hit_timestamp = now;
  		return WDRR_BUCKET_FOR_HH;
  	}
  
  	/* Now pass the packet through the multi-stage filter. */
  	tmp_hash = hash;
  	xorsum = 0;
  	for (i = 0; i < HHF_ARRAYS_CNT - 1; i++) {
  		/* Split the skb_hash into three 10-bit chunks. */
  		filter_pos[i] = tmp_hash & HHF_BIT_MASK;
  		xorsum ^= filter_pos[i];
  		tmp_hash >>= HHF_BIT_MASK_LEN;
  	}
  	/* The last chunk is computed as XOR sum of other chunks. */
  	filter_pos[HHF_ARRAYS_CNT - 1] = xorsum ^ tmp_hash;
  
  	pkt_len = qdisc_pkt_len(skb);
  	min_hhf_val = ~0U;
  	for (i = 0; i < HHF_ARRAYS_CNT; i++) {
  		u32 val;
  
  		if (!test_bit(filter_pos[i], q->hhf_valid_bits[i])) {
  			q->hhf_arrays[i][filter_pos[i]] = 0;
  			__set_bit(filter_pos[i], q->hhf_valid_bits[i]);
  		}
  
  		val = q->hhf_arrays[i][filter_pos[i]] + pkt_len;
  		if (min_hhf_val > val)
  			min_hhf_val = val;
  	}
  
  	/* Found a new HH iff all counter values > HH admit threshold. */
  	if (min_hhf_val > q->hhf_admit_bytes) {
  		/* Just captured a new heavy-hitter. */
  		flow = alloc_new_hh(&q->hh_flows[flow_pos], q);
  		if (!flow) /* memory alloc problem */
  			return WDRR_BUCKET_FOR_NON_HH;
  		flow->hash_id = hash;
  		flow->hit_timestamp = now;
  		q->hh_flows_total_cnt++;
  
  		/* By returning without updating counters in q->hhf_arrays,
  		 * we implicitly implement "shielding" (see Optimization O1).
  		 */
  		return WDRR_BUCKET_FOR_HH;
  	}
  
  	/* Conservative update of HHF arrays (see Optimization O2). */
  	for (i = 0; i < HHF_ARRAYS_CNT; i++) {
  		if (q->hhf_arrays[i][filter_pos[i]] < min_hhf_val)
  			q->hhf_arrays[i][filter_pos[i]] = min_hhf_val;
  	}
  	return WDRR_BUCKET_FOR_NON_HH;
  }
  
  /* Removes one skb from head of bucket. */
  static struct sk_buff *dequeue_head(struct wdrr_bucket *bucket)
  {
  	struct sk_buff *skb = bucket->head;
  
  	bucket->head = skb->next;
  	skb->next = NULL;
  	return skb;
  }
  
  /* Tail-adds skb to bucket. */
  static void bucket_add(struct wdrr_bucket *bucket, struct sk_buff *skb)
  {
  	if (bucket->head == NULL)
  		bucket->head = skb;
  	else
  		bucket->tail->next = skb;
  	bucket->tail = skb;
  	skb->next = NULL;
  }
  
  static unsigned int hhf_drop(struct Qdisc *sch)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	struct wdrr_bucket *bucket;
  
  	/* Always try to drop from heavy-hitters first. */
  	bucket = &q->buckets[WDRR_BUCKET_FOR_HH];
  	if (!bucket->head)
  		bucket = &q->buckets[WDRR_BUCKET_FOR_NON_HH];
  
  	if (bucket->head) {
  		struct sk_buff *skb = dequeue_head(bucket);
  
  		sch->q.qlen--;
  		sch->qstats.drops++;
  		sch->qstats.backlog -= qdisc_pkt_len(skb);
  		kfree_skb(skb);
  	}
  
  	/* Return id of the bucket from which the packet was dropped. */
  	return bucket - q->buckets;
  }
  
  static int hhf_enqueue(struct sk_buff *skb, struct Qdisc *sch)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	enum wdrr_bucket_idx idx;
  	struct wdrr_bucket *bucket;
  
  	idx = hhf_classify(skb, sch);
  
  	bucket = &q->buckets[idx];
  	bucket_add(bucket, skb);
  	sch->qstats.backlog += qdisc_pkt_len(skb);
  
  	if (list_empty(&bucket->bucketchain)) {
  		unsigned int weight;
  
  		/* The logic of new_buckets vs. old_buckets is the same as
  		 * new_flows vs. old_flows in the implementation of fq_codel,
  		 * i.e., short bursts of non-HHs should have strict priority.
  		 */
  		if (idx == WDRR_BUCKET_FOR_HH) {
  			/* Always move heavy-hitters to old bucket. */
  			weight = 1;
  			list_add_tail(&bucket->bucketchain, &q->old_buckets);
  		} else {
  			weight = q->hhf_non_hh_weight;
  			list_add_tail(&bucket->bucketchain, &q->new_buckets);
  		}
  		bucket->deficit = weight * q->quantum;
  	}
  	if (++sch->q.qlen < sch->limit)
  		return NET_XMIT_SUCCESS;
  
  	q->drop_overlimit++;
  	/* Return Congestion Notification only if we dropped a packet from this
  	 * bucket.
  	 */
  	if (hhf_drop(sch) == idx)
  		return NET_XMIT_CN;
  
  	/* As we dropped a packet, better let upper stack know this. */
  	qdisc_tree_decrease_qlen(sch, 1);
  	return NET_XMIT_SUCCESS;
  }
  
  static struct sk_buff *hhf_dequeue(struct Qdisc *sch)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	struct sk_buff *skb = NULL;
  	struct wdrr_bucket *bucket;
  	struct list_head *head;
  
  begin:
  	head = &q->new_buckets;
  	if (list_empty(head)) {
  		head = &q->old_buckets;
  		if (list_empty(head))
  			return NULL;
  	}
  	bucket = list_first_entry(head, struct wdrr_bucket, bucketchain);
  
  	if (bucket->deficit <= 0) {
  		int weight = (bucket - q->buckets == WDRR_BUCKET_FOR_HH) ?
  			      1 : q->hhf_non_hh_weight;
  
  		bucket->deficit += weight * q->quantum;
  		list_move_tail(&bucket->bucketchain, &q->old_buckets);
  		goto begin;
  	}
  
  	if (bucket->head) {
  		skb = dequeue_head(bucket);
  		sch->q.qlen--;
  		sch->qstats.backlog -= qdisc_pkt_len(skb);
  	}
  
  	if (!skb) {
  		/* Force a pass through old_buckets to prevent starvation. */
  		if ((head == &q->new_buckets) && !list_empty(&q->old_buckets))
  			list_move_tail(&bucket->bucketchain, &q->old_buckets);
  		else
  			list_del_init(&bucket->bucketchain);
  		goto begin;
  	}
  	qdisc_bstats_update(sch, skb);
  	bucket->deficit -= qdisc_pkt_len(skb);
  
  	return skb;
  }
  
  static void hhf_reset(struct Qdisc *sch)
  {
  	struct sk_buff *skb;
  
  	while ((skb = hhf_dequeue(sch)) != NULL)
  		kfree_skb(skb);
  }
  
  static void *hhf_zalloc(size_t sz)
  {
  	void *ptr = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN);
  
  	if (!ptr)
  		ptr = vzalloc(sz);
  
  	return ptr;
  }
  
  static void hhf_free(void *addr)
  {
  	if (addr) {
  		if (is_vmalloc_addr(addr))
  			vfree(addr);
  		else
  			kfree(addr);
  	}
  }
  
  static void hhf_destroy(struct Qdisc *sch)
  {
  	int i;
  	struct hhf_sched_data *q = qdisc_priv(sch);
  
  	for (i = 0; i < HHF_ARRAYS_CNT; i++) {
  		hhf_free(q->hhf_arrays[i]);
  		hhf_free(q->hhf_valid_bits[i]);
  	}
  
  	for (i = 0; i < HH_FLOWS_CNT; i++) {
  		struct hh_flow_state *flow, *next;
  		struct list_head *head = &q->hh_flows[i];
  
  		if (list_empty(head))
  			continue;
  		list_for_each_entry_safe(flow, next, head, flowchain) {
  			list_del(&flow->flowchain);
  			kfree(flow);
  		}
  	}
  	hhf_free(q->hh_flows);
  }
  
  static const struct nla_policy hhf_policy[TCA_HHF_MAX + 1] = {
  	[TCA_HHF_BACKLOG_LIMIT]	 = { .type = NLA_U32 },
  	[TCA_HHF_QUANTUM]	 = { .type = NLA_U32 },
  	[TCA_HHF_HH_FLOWS_LIMIT] = { .type = NLA_U32 },
  	[TCA_HHF_RESET_TIMEOUT]	 = { .type = NLA_U32 },
  	[TCA_HHF_ADMIT_BYTES]	 = { .type = NLA_U32 },
  	[TCA_HHF_EVICT_TIMEOUT]	 = { .type = NLA_U32 },
  	[TCA_HHF_NON_HH_WEIGHT]	 = { .type = NLA_U32 },
  };
  
  static int hhf_change(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	struct nlattr *tb[TCA_HHF_MAX + 1];
  	unsigned int qlen;
  	int err;
  	u64 non_hh_quantum;
  	u32 new_quantum = q->quantum;
  	u32 new_hhf_non_hh_weight = q->hhf_non_hh_weight;
  
  	if (!opt)
  		return -EINVAL;
  
  	err = nla_parse_nested(tb, TCA_HHF_MAX, opt, hhf_policy);
  	if (err < 0)
  		return err;
  
  	if (tb[TCA_HHF_QUANTUM])
  		new_quantum = nla_get_u32(tb[TCA_HHF_QUANTUM]);
  
  	if (tb[TCA_HHF_NON_HH_WEIGHT])
  		new_hhf_non_hh_weight = nla_get_u32(tb[TCA_HHF_NON_HH_WEIGHT]);
  
  	non_hh_quantum = (u64)new_quantum * new_hhf_non_hh_weight;
  	if (non_hh_quantum > INT_MAX)
  		return -EINVAL;
  
  	sch_tree_lock(sch);
  
  	if (tb[TCA_HHF_BACKLOG_LIMIT])
  		sch->limit = nla_get_u32(tb[TCA_HHF_BACKLOG_LIMIT]);
  
  	q->quantum = new_quantum;
  	q->hhf_non_hh_weight = new_hhf_non_hh_weight;
  
  	if (tb[TCA_HHF_HH_FLOWS_LIMIT])
  		q->hh_flows_limit = nla_get_u32(tb[TCA_HHF_HH_FLOWS_LIMIT]);
  
  	if (tb[TCA_HHF_RESET_TIMEOUT]) {
  		u32 us = nla_get_u32(tb[TCA_HHF_RESET_TIMEOUT]);
  
  		q->hhf_reset_timeout = usecs_to_jiffies(us);
  	}
  
  	if (tb[TCA_HHF_ADMIT_BYTES])
  		q->hhf_admit_bytes = nla_get_u32(tb[TCA_HHF_ADMIT_BYTES]);
  
  	if (tb[TCA_HHF_EVICT_TIMEOUT]) {
  		u32 us = nla_get_u32(tb[TCA_HHF_EVICT_TIMEOUT]);
  
  		q->hhf_evict_timeout = usecs_to_jiffies(us);
  	}
  
  	qlen = sch->q.qlen;
  	while (sch->q.qlen > sch->limit) {
  		struct sk_buff *skb = hhf_dequeue(sch);
  
  		kfree_skb(skb);
  	}
  	qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);
  
  	sch_tree_unlock(sch);
  	return 0;
  }
  
  static int hhf_init(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	int i;
  
  	sch->limit = 1000;
  	q->quantum = psched_mtu(qdisc_dev(sch));
  	q->perturbation = prandom_u32();
  	INIT_LIST_HEAD(&q->new_buckets);
  	INIT_LIST_HEAD(&q->old_buckets);
  
  	/* Configurable HHF parameters */
  	q->hhf_reset_timeout = HZ / 25; /* 40  ms */
  	q->hhf_admit_bytes = 131072;    /* 128 KB */
  	q->hhf_evict_timeout = HZ;      /* 1  sec */
  	q->hhf_non_hh_weight = 2;
  
  	if (opt) {
  		int err = hhf_change(sch, opt);
  
  		if (err)
  			return err;
  	}
  
  	if (!q->hh_flows) {
  		/* Initialize heavy-hitter flow table. */
  		q->hh_flows = hhf_zalloc(HH_FLOWS_CNT *
  					 sizeof(struct list_head));
  		if (!q->hh_flows)
  			return -ENOMEM;
  		for (i = 0; i < HH_FLOWS_CNT; i++)
  			INIT_LIST_HEAD(&q->hh_flows[i]);
  
  		/* Cap max active HHs at twice len of hh_flows table. */
  		q->hh_flows_limit = 2 * HH_FLOWS_CNT;
  		q->hh_flows_overlimit = 0;
  		q->hh_flows_total_cnt = 0;
  		q->hh_flows_current_cnt = 0;
  
  		/* Initialize heavy-hitter filter arrays. */
  		for (i = 0; i < HHF_ARRAYS_CNT; i++) {
  			q->hhf_arrays[i] = hhf_zalloc(HHF_ARRAYS_LEN *
  						      sizeof(u32));
  			if (!q->hhf_arrays[i]) {
  				hhf_destroy(sch);
  				return -ENOMEM;
  			}
  		}
  		q->hhf_arrays_reset_timestamp = hhf_time_stamp();
  
  		/* Initialize valid bits of heavy-hitter filter arrays. */
  		for (i = 0; i < HHF_ARRAYS_CNT; i++) {
  			q->hhf_valid_bits[i] = hhf_zalloc(HHF_ARRAYS_LEN /
  							  BITS_PER_BYTE);
  			if (!q->hhf_valid_bits[i]) {
  				hhf_destroy(sch);
  				return -ENOMEM;
  			}
  		}
  
  		/* Initialize Weighted DRR buckets. */
  		for (i = 0; i < WDRR_BUCKET_CNT; i++) {
  			struct wdrr_bucket *bucket = q->buckets + i;
  
  			INIT_LIST_HEAD(&bucket->bucketchain);
  		}
  	}
  
  	return 0;
  }
  
  static int hhf_dump(struct Qdisc *sch, struct sk_buff *skb)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	struct nlattr *opts;
  
  	opts = nla_nest_start(skb, TCA_OPTIONS);
  	if (opts == NULL)
  		goto nla_put_failure;
  
  	if (nla_put_u32(skb, TCA_HHF_BACKLOG_LIMIT, sch->limit) ||
  	    nla_put_u32(skb, TCA_HHF_QUANTUM, q->quantum) ||
  	    nla_put_u32(skb, TCA_HHF_HH_FLOWS_LIMIT, q->hh_flows_limit) ||
  	    nla_put_u32(skb, TCA_HHF_RESET_TIMEOUT,
  			jiffies_to_usecs(q->hhf_reset_timeout)) ||
  	    nla_put_u32(skb, TCA_HHF_ADMIT_BYTES, q->hhf_admit_bytes) ||
  	    nla_put_u32(skb, TCA_HHF_EVICT_TIMEOUT,
  			jiffies_to_usecs(q->hhf_evict_timeout)) ||
  	    nla_put_u32(skb, TCA_HHF_NON_HH_WEIGHT, q->hhf_non_hh_weight))
  		goto nla_put_failure;
  
  	nla_nest_end(skb, opts);
  	return skb->len;
  
  nla_put_failure:
  	return -1;
  }
  
  static int hhf_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
  {
  	struct hhf_sched_data *q = qdisc_priv(sch);
  	struct tc_hhf_xstats st = {
  		.drop_overlimit = q->drop_overlimit,
  		.hh_overlimit	= q->hh_flows_overlimit,
  		.hh_tot_count	= q->hh_flows_total_cnt,
  		.hh_cur_count	= q->hh_flows_current_cnt,
  	};
  
  	return gnet_stats_copy_app(d, &st, sizeof(st));
  }
  
  static struct Qdisc_ops hhf_qdisc_ops __read_mostly = {
  	.id		=	"hhf",
  	.priv_size	=	sizeof(struct hhf_sched_data),
  
  	.enqueue	=	hhf_enqueue,
  	.dequeue	=	hhf_dequeue,
  	.peek		=	qdisc_peek_dequeued,
  	.drop		=	hhf_drop,
  	.init		=	hhf_init,
  	.reset		=	hhf_reset,
  	.destroy	=	hhf_destroy,
  	.change		=	hhf_change,
  	.dump		=	hhf_dump,
  	.dump_stats	=	hhf_dump_stats,
  	.owner		=	THIS_MODULE,
  };
  
  static int __init hhf_module_init(void)
  {
  	return register_qdisc(&hhf_qdisc_ops);
  }
  
  static void __exit hhf_module_exit(void)
  {
  	unregister_qdisc(&hhf_qdisc_ops);
  }
  
  module_init(hhf_module_init)
  module_exit(hhf_module_exit)
  MODULE_AUTHOR("Terry Lam");
  MODULE_AUTHOR("Nandita Dukkipati");
  MODULE_LICENSE("GPL");