diff options
| author | John Fastabend <john.fastabend@gmail.com> | 2018-03-24 22:25:06 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2018-03-26 12:36:23 -0400 |
| commit | eb82a994479245a79647d302f9b4eb8e7c9d7ca6 (patch) | |
| tree | f2b46c8bc079ea5f443c9ecbd082e053b39c0f42 /net/sched | |
| parent | 743989254ea9f132517806d8893ca9b6cf9dc86b (diff) | |
net: sched, fix OOO packets with pfifo_fast
After the qdisc lock was dropped in pfifo_fast we allow multiple
enqueue threads and dequeue threads to run in parallel. On the
enqueue side the skb bit ooo_okay is used to ensure all related
skbs are enqueued in-order. On the dequeue side though there is
no similar logic. What we observe is with fewer queues than CPUs
it is possible to re-order packets when two instances of
__qdisc_run() are running in parallel. Each thread will dequeue
a skb and then whichever thread calls the ndo op first will
be sent on the wire. This doesn't typically happen because
qdisc_run() is usually triggered by the same core that did the
enqueue. However, drivers will trigger __netif_schedule()
when queues are transitioning from stopped to awake using the
netif_tx_wake_* APIs. When this happens netif_schedule() calls
qdisc_run() on the same CPU that did the netif_tx_wake_* which
is usually done in the interrupt completion context. This CPU
is selected with the irq affinity which is unrelated to the
enqueue operations.
To resolve this we add a RUNNING bit to the qdisc to ensure
only a single dequeue per qdisc is running. Enqueue and dequeue
operations can still run in parallel and also on multi queue
NICs we can still have a dequeue in-flight per qdisc, which
is typically per CPU.
Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
Reported-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
| -rw-r--r-- | net/sched/sch_generic.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 7e3fbe9cc936..39c144b6ff98 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -373,24 +373,33 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, */ static inline bool qdisc_restart(struct Qdisc *q, int *packets) { + bool more, validate, nolock = q->flags & TCQ_F_NOLOCK; spinlock_t *root_lock = NULL; struct netdev_queue *txq; struct net_device *dev; struct sk_buff *skb; - bool validate; /* Dequeue packet */ + if (nolock && test_and_set_bit(__QDISC_STATE_RUNNING, &q->state)) + return false; + skb = dequeue_skb(q, &validate, packets); - if (unlikely(!skb)) + if (unlikely(!skb)) { + if (nolock) + clear_bit(__QDISC_STATE_RUNNING, &q->state); return false; + } - if (!(q->flags & TCQ_F_NOLOCK)) + if (!nolock) root_lock = qdisc_lock(q); dev = qdisc_dev(q); txq = skb_get_tx_queue(dev, skb); - return sch_direct_xmit(skb, q, dev, txq, root_lock, validate); + more = sch_direct_xmit(skb, q, dev, txq, root_lock, validate); + if (nolock) + clear_bit(__QDISC_STATE_RUNNING, &q->state); + return more; } void __qdisc_run(struct Qdisc *q) |