net_sched: RCU conversion of stab
This patch converts stab qdisc management to RCU, so that we can perform
the qdisc_calculate_pkt_len() call before getting qdisc lock.
This shortens the lock's held time in __dev_xmit_skb().
This permits more qdiscs to get TCQ_F_CAN_BYPASS status, avoiding lot of
cache misses and so reducing latencies.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jesper Dangaard Brouer <hawk@diku.dk>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index a4ccd47..2730352 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2325,15 +2325,18 @@
struct netdev_queue *txq)
{
spinlock_t *root_lock = qdisc_lock(q);
- bool contended = qdisc_is_running(q);
+ bool contended;
int rc;
+ qdisc_skb_cb(skb)->pkt_len = skb->len;
+ qdisc_calculate_pkt_len(skb, q);
/*
* Heuristic to force contended enqueues to serialize on a
* separate lock before trying to get qdisc main lock.
* This permits __QDISC_STATE_RUNNING owner to get the lock more often
* and dequeue packets faster.
*/
+ contended = qdisc_is_running(q);
if (unlikely(contended))
spin_lock(&q->busylock);
@@ -2351,7 +2354,6 @@
if (!(dev->priv_flags & IFF_XMIT_DST_RELEASE))
skb_dst_force(skb);
- qdisc_skb_cb(skb)->pkt_len = skb->len;
qdisc_bstats_update(q, skb);
if (sch_direct_xmit(skb, q, dev, txq, root_lock)) {
@@ -2366,7 +2368,7 @@
rc = NET_XMIT_SUCCESS;
} else {
skb_dst_force(skb);
- rc = qdisc_enqueue_root(skb, q);
+ rc = q->enqueue(skb, q) & NET_XMIT_MASK;
if (qdisc_run_begin(q)) {
if (unlikely(contended)) {
spin_unlock(&q->busylock);