Currently pfifo_fast has both TCQ_F_CAN_BYPASS and TCQ_F_NOLOCK
flag set, but queue discipline by-pass does not work for lockless
qdisc because skb is always enqueued to qdisc even when the qdisc
is empty, see __dev_xmit_skb().
This patch calls sch_direct_xmit() to transmit the skb directly
to the driver for empty lockless qdisc too, which aviod enqueuing
and dequeuing operation. qdisc->empty is set to false whenever a
skb is enqueued, see pfifo_fast_enqueue(), and is set to true when
skb dequeuing return NULL, see pfifo_fast_dequeue(), a spinlock is
added to avoid the race between enqueue/dequeue and qdisc->empty
setting.
If there is requeued skb in q->gso_skb, and qdisc->empty is true,
do not allow bypassing requeued skb. enqueuing and dequeuing in
q->gso_skb is always protected by qdisc->seqlock, so is the access
of q->gso_skb by skb_queue_empty();
Also, qdisc is scheduled at the end of qdisc_run_end() when q->empty
is false to avoid packet stuck problem.
The performance for ip_forward test increases about 10% with this
patch.
Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
---
RFC V2: fix requeued skb out of order and data race problem.
---
include/net/pkt_sched.h | 2 ++
include/net/sch_generic.h | 7 +++++--
net/core/dev.c | 14 ++++++++++++++
net/sched/sch_generic.c | 31 ++++++++++++++++++++++++++++++-
4 files changed, 51 insertions(+), 3 deletions(-)
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index f5c1bee..c760f6a 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -122,6 +122,8 @@ void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc);
bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
struct net_device *dev, struct netdev_queue *txq,
spinlock_t *root_lock, bool validate);
+bool sch_may_need_requeuing(struct sk_buff *skb, struct Qdisc *q,
+ struct net_device *dev);
void __qdisc_run(struct Qdisc *q);
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 2d6eb60..6591356 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -161,7 +161,6 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
if (qdisc->flags & TCQ_F_NOLOCK) {
if (!spin_trylock(&qdisc->seqlock))
return false;
- WRITE_ONCE(qdisc->empty, false);
} else if (qdisc_is_running(qdisc)) {
return false;
}
@@ -176,8 +175,12 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
static inline void qdisc_run_end(struct Qdisc *qdisc)
{
write_seqcount_end(&qdisc->running);
- if (qdisc->flags & TCQ_F_NOLOCK)
+ if (qdisc->flags & TCQ_F_NOLOCK) {
spin_unlock(&qdisc->seqlock);
+
+ if (unlikely(!READ_ONCE(qdisc->empty)))
+ __netif_schedule(qdisc);
+ }
}
static inline bool qdisc_may_bulk(const struct Qdisc *qdisc)
diff --git a/net/core/dev.c b/net/core/dev.c
index 2bfdd52..8f4afb6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3791,6 +3791,20 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
qdisc_calculate_pkt_len(skb, q);
if (q->flags & TCQ_F_NOLOCK) {
+ if (q->flags & TCQ_F_CAN_BYPASS && READ_ONCE(q->empty) &&
+ qdisc_run_begin(q)) {
+ qdisc_bstats_cpu_update(q, skb);
+
+ if (sch_may_need_requeuing(skb, q, dev))
+ __qdisc_run(q);
+ else if (sch_direct_xmit(skb, q, dev, txq, NULL, true) &&
+ !READ_ONCE(q->empty))
+ __qdisc_run(q);
+
+ qdisc_run_end(q);
+ return NET_XMIT_SUCCESS;
+ }
+
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
qdisc_run(q);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 49eae93..0df1462 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -273,6 +273,23 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
return skb;
}
+bool sch_may_need_requeuing(struct sk_buff *skb, struct Qdisc *q,
+ struct net_device *dev)
+{
+ bool again = false;
+
+ if (likely(skb_queue_empty(&q->gso_skb)))
+ return false;
+
+ /* need validating before requeuing */
+ skb = validate_xmit_skb_list(skb, dev, &again);
+ if (unlikely(!skb))
+ return true;
+
+ dev_requeue_skb(skb, q);
+ return true;
+}
+
/*
* Transmit possibly several skbs, and handle the return status as
* required. Owning running seqcount bit guarantees that
@@ -606,6 +623,11 @@ static const u8 prio2band[TC_PRIO_MAX + 1] = {
*/
struct pfifo_fast_priv {
struct skb_array q[PFIFO_FAST_BANDS];
+
+ /* protect against data race between enqueue/dequeue and
+ * qdisc->empty setting
+ */
+ spinlock_t lock;
};
static inline struct skb_array *band2list(struct pfifo_fast_priv *priv,
@@ -623,7 +645,10 @@ static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc,
unsigned int pkt_len = qdisc_pkt_len(skb);
int err;
- err = skb_array_produce(q, skb);
+ spin_lock(&priv->lock);
+ err = __ptr_ring_produce(&q->ring, skb);
+ WRITE_ONCE(qdisc->empty, false);
+ spin_unlock(&priv->lock);
if (unlikely(err)) {
if (qdisc_is_percpu_stats(qdisc))
@@ -642,6 +667,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
struct sk_buff *skb = NULL;
int band;
+ spin_lock(&priv->lock);
for (band = 0; band < PFIFO_FAST_BANDS && !skb; band++) {
struct skb_array *q = band2list(priv, band);
@@ -655,6 +681,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
} else {
WRITE_ONCE(qdisc->empty, true);
}
+ spin_unlock(&priv->lock);
return skb;
}
@@ -739,6 +766,8 @@ static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt,
/* Can by-pass the queue discipline */
qdisc->flags |= TCQ_F_CAN_BYPASS;
+
+ spin_lock_init(&priv->lock);
return 0;
}
--
2.7.4
