On 15.03.21 04:10, Yunsheng Lin wrote: > 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. cansequence didn't find any frame reordering with 2 FlexCAN's communicating with each other on a dual core i.MX6. Feel free to add: Tested-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> > --- > 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; > } > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |