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sched: add and use qdisc_skb_head helpers
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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>
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Florian Westphal authored and David S. Miller committed Sep 19, 2016
1 parent ed760cb commit 48da34b
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Showing 4 changed files with 94 additions and 28 deletions.
63 changes: 51 additions & 12 deletions include/net/sch_generic.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand All @@ -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;
}
Expand All @@ -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);
Expand All @@ -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 */
Expand Down Expand Up @@ -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;
}
}

Expand Down
21 changes: 11 additions & 10 deletions net/sched/sch_generic.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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];
};

/*
Expand All @@ -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;
Expand All @@ -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++;
Expand All @@ -505,16 +505,16 @@ 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);
qdisc_bstats_update(qdisc, skb);
}

qdisc->q.qlen--;
if (skb_queue_empty(list))
if (qh->qlen == 0)
priv->bitmap &= ~(1 << band);

return skb;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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,
Expand Down
24 changes: 20 additions & 4 deletions net/sched/sch_htb.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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)
{
Expand All @@ -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);
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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]);
Expand Down
14 changes: 12 additions & 2 deletions net/sched/sch_netem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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++;
}

Expand Down

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