sched: manipulate __QDISC_STATE_RUNNING in qdisc_run_* helpers
Currently NOLOCK qdiscs pay a measurable overhead to atomically
manipulate the __QDISC_STATE_RUNNING. Such bit is flipped twice per
packet in the uncontended scenario with packet rate below the
line rate: on packed dequeue and on the next, failing dequeue attempt.
This changeset moves the bit manipulation into the qdisc_run_{begin,end}
helpers, so that the bit is now flipped only once per packet, with
measurable performance improvement in the uncontended scenario.
This also allows simplifying the qdisc teardown code path - since
qdisc_is_running() is now effective for each qdisc type - and avoid a
possible race between qdisc_run() and dev_deactivate_many(), as now
the some_qdisc_is_busy() can properly detect NOLOCK qdiscs being busy
dequeuing packets.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 39c144b..ff3ce71 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -373,33 +373,24 @@ 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 (nolock)
- clear_bit(__QDISC_STATE_RUNNING, &q->state);
+ if (unlikely(!skb))
return false;
- }
- if (!nolock)
+ if (!(q->flags & TCQ_F_NOLOCK))
root_lock = qdisc_lock(q);
dev = qdisc_dev(q);
txq = skb_get_tx_queue(dev, skb);
- more = sch_direct_xmit(skb, q, dev, txq, root_lock, validate);
- if (nolock)
- clear_bit(__QDISC_STATE_RUNNING, &q->state);
- return more;
+ return sch_direct_xmit(skb, q, dev, txq, root_lock, validate);
}
void __qdisc_run(struct Qdisc *q)
@@ -1131,17 +1122,13 @@ static bool some_qdisc_is_busy(struct net_device *dev)
dev_queue = netdev_get_tx_queue(dev, i);
q = dev_queue->qdisc_sleeping;
- if (q->flags & TCQ_F_NOLOCK) {
- val = test_bit(__QDISC_STATE_SCHED, &q->state);
- } else {
- root_lock = qdisc_lock(q);
- spin_lock_bh(root_lock);
+ root_lock = qdisc_lock(q);
+ spin_lock_bh(root_lock);
- val = (qdisc_is_running(q) ||
- test_bit(__QDISC_STATE_SCHED, &q->state));
+ val = (qdisc_is_running(q) ||
+ test_bit(__QDISC_STATE_SCHED, &q->state));
- spin_unlock_bh(root_lock);
- }
+ spin_unlock_bh(root_lock);
if (val)
return true;