The netdev qeueue might be stopped when byte queue limit has reached or tx hw ring is full, net_tx_action() may still be rescheduled endlessly if STATE_MISSED is set, which consumes a lot of cpu without dequeuing and transmiting any skb because the netdev queue is stopped, see qdisc_run_end().
This patch fixes it by checking the netdev queue state before calling qdisc_run() and clearing STATE_MISSED if netdev queue is stopped during qdisc_run(), the net_tx_action() is recheduled again when netdev qeueue is restarted, see netif_tx_wake_queue().
Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking") Reported-by: Michal Kubecek mkubecek@suse.cz Signed-off-by: Yunsheng Lin linyunsheng@huawei.com --- V6: Drop NET_XMIT_DROP checking for it is not really relevant to this patch, and it may cause performance performance regression with multi pktgen threads on dummy netdev with pfifo_fast qdisc case. --- net/core/dev.c | 3 ++- net/sched/sch_generic.c | 8 +++++++- 2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c index d596cd7..ef8cf76 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3853,7 +3853,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
if (q->flags & TCQ_F_NOLOCK) { rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK; - qdisc_run(q); + if (likely(!netif_xmit_frozen_or_stopped(txq))) + qdisc_run(q);
if (unlikely(to_free)) kfree_skb_list(to_free); diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index d86c4cc..37403c1 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -74,6 +74,7 @@ static inline struct sk_buff *__skb_dequeue_bad_txq(struct Qdisc *q) } } else { skb = SKB_XOFF_MAGIC; + clear_bit(__QDISC_STATE_MISSED, &q->state); } }
@@ -242,6 +243,7 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate, } } else { skb = NULL; + clear_bit(__QDISC_STATE_MISSED, &q->state); } if (lock) spin_unlock(lock); @@ -251,8 +253,10 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate, *validate = true;
if ((q->flags & TCQ_F_ONETXQUEUE) && - netif_xmit_frozen_or_stopped(txq)) + netif_xmit_frozen_or_stopped(txq)) { + clear_bit(__QDISC_STATE_MISSED, &q->state); return skb; + }
skb = qdisc_dequeue_skb_bad_txq(q); if (unlikely(skb)) { @@ -311,6 +315,8 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, HARD_TX_LOCK(dev, txq, smp_processor_id()); if (!netif_xmit_frozen_or_stopped(txq)) skb = dev_hard_start_xmit(skb, dev, txq, &ret); + else + clear_bit(__QDISC_STATE_MISSED, &q->state);
HARD_TX_UNLOCK(dev, txq); } else {