On Mon, 10 May 2021 09:42:36 +0800 Yunsheng Lin wrote:
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 <redacted>
Signed-off-by: Yunsheng Lin <redacted>
Patches 1 and 2 look good to me but this one I'm not 100% sure.
quoted hunk ↗ jump to hunk
@@ -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;
+ }
The queues are woken asynchronously without holding any locks via
netif_tx_wake_queue(). Theoretically we can have a situation where:
CPU 0 CPU 1
. .
dequeue_skb() .
netif_xmit_frozen..() # true .
. [IRQ]
. netif_tx_wake_queue()
. <end of IRQ>
. netif_tx_action()
. set MISSED
clear MISSED
return NULL
ret from qdisc_restart()
ret from __qdisc_run()
qdisc_run_end()
-> MISSED not set