sched: add and use qdisc_skb_head helpers

This change replaces sk_buff_head struct in Qdiscs with new qdisc_skb_head.

Its similar to the skb_buff_head api, but does not use skb->prev pointers.

Qdiscs will commonly enqueue at the tail of a list and dequeue at head.
While skb_buff_head works fine for this, enqueue/dequeue needs to also
adjust the prev pointer of next element.

The ->prev pointer is not required for qdiscs so we can just leave
it undefined and avoid one cacheline write access for en/dequeue.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 0741ed4..e6aa0a2 100644 (file)
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -36,6 +36,14 @@ struct qdisc_size_table {
        u16                     data[];
 };
 
+/* similar to sk_buff_head, but skb->prev pointer is undefined. */
+struct qdisc_skb_head {
+       struct sk_buff  *head;
+       struct sk_buff  *tail;
+       __u32           qlen;
+       spinlock_t      lock;
+};
+
 struct Qdisc {
        int                     (*enqueue)(struct sk_buff *skb,
                                           struct Qdisc *sch,
@@ -76,7 +84,7 @@ struct Qdisc {
         * For performance sake on SMP, we put highly modified fields at the end
         */
        struct sk_buff          *gso_skb ____cacheline_aligned_in_smp;
-       struct sk_buff_head     q;
+       struct qdisc_skb_head   q;
        struct gnet_stats_basic_packed bstats;
        seqcount_t              running;
        struct gnet_stats_queue qstats;
@@ -600,10 +608,27 @@ static inline void qdisc_qstats_overlimit(struct Qdisc *sch)
        sch->qstats.overlimits++;
 }
 
+static inline void qdisc_skb_head_init(struct qdisc_skb_head *qh)
+{
+       qh->head = NULL;
+       qh->tail = NULL;
+       qh->qlen = 0;
+}
+
 static inline int __qdisc_enqueue_tail(struct sk_buff *skb, struct Qdisc *sch,
-                                      struct sk_buff_head *list)
+                                      struct qdisc_skb_head *qh)
 {
-       __skb_queue_tail(list, skb);
+       struct sk_buff *last = qh->tail;
+
+       if (last) {
+               skb->next = NULL;
+               last->next = skb;
+               qh->tail = skb;
+       } else {
+               qh->tail = skb;
+               qh->head = skb;
+       }
+       qh->qlen++;
        qdisc_qstats_backlog_inc(sch, skb);
 
        return NET_XMIT_SUCCESS;
@@ -614,9 +639,17 @@ static inline int qdisc_enqueue_tail(struct sk_buff *skb, struct Qdisc *sch)
        return __qdisc_enqueue_tail(skb, sch, &sch->q);
 }
 
-static inline struct sk_buff *__qdisc_dequeue_head(struct sk_buff_head *list)
+static inline struct sk_buff *__qdisc_dequeue_head(struct qdisc_skb_head *qh)
 {
-       struct sk_buff *skb = __skb_dequeue(list);
+       struct sk_buff *skb = qh->head;
+
+       if (likely(skb != NULL)) {
+               qh->head = skb->next;
+               qh->qlen--;
+               if (qh->head == NULL)
+                       qh->tail = NULL;
+               skb->next = NULL;
+       }
 
        return skb;
 }
@@ -643,10 +676,10 @@ static inline void __qdisc_drop(struct sk_buff *skb, struct sk_buff **to_free)
 }
 
 static inline unsigned int __qdisc_queue_drop_head(struct Qdisc *sch,
-                                                  struct sk_buff_head *list,
+                                                  struct qdisc_skb_head *qh,
                                                   struct sk_buff **to_free)
 {
-       struct sk_buff *skb = __skb_dequeue(list);
+       struct sk_buff *skb = __qdisc_dequeue_head(qh);
 
        if (likely(skb != NULL)) {
                unsigned int len = qdisc_pkt_len(skb);
@@ -667,7 +700,9 @@ static inline unsigned int qdisc_queue_drop_head(struct Qdisc *sch,
 
 static inline struct sk_buff *qdisc_peek_head(struct Qdisc *sch)
 {
-       return skb_peek(&sch->q);
+       const struct qdisc_skb_head *qh = &sch->q;
+
+       return qh->head;
 }
 
 /* generic pseudo peek method for non-work-conserving qdisc */
@@ -702,15 +737,19 @@ static inline struct sk_buff *qdisc_dequeue_peeked(struct Qdisc *sch)
        return skb;
 }
 
-static inline void __qdisc_reset_queue(struct sk_buff_head *list)
+static inline void __qdisc_reset_queue(struct qdisc_skb_head *qh)
 {
        /*
         * We do not know the backlog in bytes of this list, it
         * is up to the caller to correct it
         */
-       if (!skb_queue_empty(list)) {
-               rtnl_kfree_skbs(list->next, list->prev);
-               __skb_queue_head_init(list);
+       ASSERT_RTNL();
+       if (qh->qlen) {
+               rtnl_kfree_skbs(qh->head, qh->tail);
+
+               qh->head = NULL;
+               qh->tail = NULL;
+               qh->qlen = 0;
        }
 }
 

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 73877d9..6cfb6e9 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -466,7 +466,7 @@ static const u8 prio2band[TC_PRIO_MAX + 1] = {
  */
 struct pfifo_fast_priv {
        u32 bitmap;
-       struct sk_buff_head q[PFIFO_FAST_BANDS];
+       struct qdisc_skb_head q[PFIFO_FAST_BANDS];
 };
 
 /*
@@ -477,7 +477,7 @@ struct pfifo_fast_priv {
  */
 static const int bitmap2band[] = {-1, 0, 1, 0, 2, 0, 1, 0};
 
-static inline struct sk_buff_head *band2list(struct pfifo_fast_priv *priv,
+static inline struct qdisc_skb_head *band2list(struct pfifo_fast_priv *priv,
                                             int band)
 {
        return priv->q + band;
@@ -489,7 +489,7 @@ static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc,
        if (qdisc->q.qlen < qdisc_dev(qdisc)->tx_queue_len) {
                int band = prio2band[skb->priority & TC_PRIO_MAX];
                struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
-               struct sk_buff_head *list = band2list(priv, band);
+               struct qdisc_skb_head *list = band2list(priv, band);
 
                priv->bitmap |= (1 << band);
                qdisc->q.qlen++;
@@ -505,8 +505,8 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
        int band = bitmap2band[priv->bitmap];
 
        if (likely(band >= 0)) {
-               struct sk_buff_head *list = band2list(priv, band);
-               struct sk_buff *skb = __qdisc_dequeue_head(list);
+               struct qdisc_skb_head *qh = band2list(priv, band);
+               struct sk_buff *skb = __qdisc_dequeue_head(qh);
 
                if (likely(skb != NULL)) {
                        qdisc_qstats_backlog_dec(qdisc, skb);
@@ -514,7 +514,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
                }
 
                qdisc->q.qlen--;
-               if (skb_queue_empty(list))
+               if (qh->qlen == 0)
                        priv->bitmap &= ~(1 << band);
 
                return skb;
@@ -529,9 +529,9 @@ static struct sk_buff *pfifo_fast_peek(struct Qdisc *qdisc)
        int band = bitmap2band[priv->bitmap];
 
        if (band >= 0) {
-               struct sk_buff_head *list = band2list(priv, band);
+               struct qdisc_skb_head *qh = band2list(priv, band);
 
-               return skb_peek(list);
+               return qh->head;
        }
 
        return NULL;
@@ -569,7 +569,7 @@ static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt)
        struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
 
        for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
-               __skb_queue_head_init(band2list(priv, prio));
+               qdisc_skb_head_init(band2list(priv, prio));
 
        /* Can by-pass the queue discipline */
        qdisc->flags |= TCQ_F_CAN_BYPASS;
@@ -617,7 +617,8 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
                sch = (struct Qdisc *) QDISC_ALIGN((unsigned long) p);
                sch->padded = (char *) sch - (char *) p;
        }
-       skb_queue_head_init(&sch->q);
+       qdisc_skb_head_init(&sch->q);
+       spin_lock_init(&sch->q.lock);
 
        spin_lock_init(&sch->busylock);
        lockdep_set_class(&sch->busylock,

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 53dbfa1..c798d0d 100644 (file)
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -162,7 +162,7 @@ struct htb_sched {
        struct work_struct      work;
 
        /* non shaped skbs; let them go directly thru */
-       struct sk_buff_head     direct_queue;
+       struct qdisc_skb_head   direct_queue;
        long                    direct_pkts;
 
        struct qdisc_watchdog   watchdog;
@@ -570,6 +570,22 @@ static inline void htb_deactivate(struct htb_sched *q, struct htb_class *cl)
        list_del_init(&cl->un.leaf.drop_list);
 }
 
+static void htb_enqueue_tail(struct sk_buff *skb, struct Qdisc *sch,
+                            struct qdisc_skb_head *qh)
+{
+       struct sk_buff *last = qh->tail;
+
+       if (last) {
+               skb->next = NULL;
+               last->next = skb;
+               qh->tail = skb;
+       } else {
+               qh->tail = skb;
+               qh->head = skb;
+       }
+       qh->qlen++;
+}
+
 static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                       struct sk_buff **to_free)
 {
@@ -580,7 +596,7 @@ static int htb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
        if (cl == HTB_DIRECT) {
                /* enqueue to helper queue */
                if (q->direct_queue.qlen < q->direct_qlen) {
-                       __skb_queue_tail(&q->direct_queue, skb);
+                       htb_enqueue_tail(skb, sch, &q->direct_queue);
                        q->direct_pkts++;
                } else {
                        return qdisc_drop(skb, sch, to_free);
@@ -888,7 +904,7 @@ static struct sk_buff *htb_dequeue(struct Qdisc *sch)
        unsigned long start_at;
 
        /* try to dequeue direct packets as high prio (!) to minimize cpu work */
-       skb = __skb_dequeue(&q->direct_queue);
+       skb = __qdisc_dequeue_head(&q->direct_queue);
        if (skb != NULL) {
 ok:
                qdisc_bstats_update(sch, skb);
@@ -1019,7 +1035,7 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt)
 
        qdisc_watchdog_init(&q->watchdog, sch);
        INIT_WORK(&q->work, htb_work_func);
-       __skb_queue_head_init(&q->direct_queue);
+       qdisc_skb_head_init(&q->direct_queue);
 
        if (tb[TCA_HTB_DIRECT_QLEN])
                q->direct_qlen = nla_get_u32(tb[TCA_HTB_DIRECT_QLEN]);

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 0a964b3..9f7b380 100644 (file)
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -413,6 +413,16 @@ static struct sk_buff *netem_segment(struct sk_buff *skb, struct Qdisc *sch,
        return segs;
 }
 
+static void netem_enqueue_skb_head(struct qdisc_skb_head *qh, struct sk_buff *skb)
+{
+       skb->next = qh->head;
+
+       if (!qh->head)
+               qh->tail = skb;
+       qh->head = skb;
+       qh->qlen++;
+}
+
 /*
  * Insert one skb into qdisc.
  * Note: parent depends on return value to account for queue length.
@@ -523,7 +533,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                        struct sk_buff *last;
 
                        if (sch->q.qlen)
-                               last = skb_peek_tail(&sch->q);
+                               last = sch->q.tail;
                        else
                                last = netem_rb_to_skb(rb_last(&q->t_root));
                        if (last) {
@@ -552,7 +562,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                cb->time_to_send = psched_get_time();
                q->counter = 0;
 
-               __skb_queue_head(&sch->q, skb);
+               netem_enqueue_skb_head(&sch->q, skb);
                sch->qstats.requeues++;
        }