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authorKrishna Kumar <krkumar2@in.ibm.com>2009-08-06 01:44:21 +0000
committerDavid S. Miller <davem@davemloft.net>2009-08-06 20:10:18 -0700
commitbbd8a0d3a3b65d341437f8b99c828fa5cc29c739 (patch)
treea4055c65be5ce3f8fd4987a32a38dfab1642ec95 /include/net/pkt_sched.h
parent9f519f68cfffba022978634f724944a0b971fec1 (diff)
net: Avoid enqueuing skb for default qdiscs
dev_queue_xmit enqueue's a skb and calls qdisc_run which dequeue's the skb and xmits it. In most cases, the skb that is enqueue'd is the same one that is dequeue'd (unless the queue gets stopped or multiple cpu's write to the same queue and ends in a race with qdisc_run). For default qdiscs, we can remove the redundant enqueue/dequeue and simply xmit the skb since the default qdisc is work-conserving. The patch uses a new flag - TCQ_F_CAN_BYPASS to identify the default fast queue. The controversial part of the patch is incrementing qlen when a skb is requeued - this is to avoid checks like the second line below: + } else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q) && >> !q->gso_skb && + !test_and_set_bit(__QDISC_STATE_RUNNING, &q->state)) { Results of a 2 hour testing for multiple netperf sessions (1, 2, 4, 8, 12 sessions on a 4 cpu system-X). The BW numbers are aggregate Mb/s across iterations tested with this version on System-X boxes with Chelsio 10gbps cards: ---------------------------------- Size | ORG BW NEW BW | ---------------------------------- 128K | 156964 159381 | 256K | 158650 162042 | ---------------------------------- Changes from ver1: 1. Move sch_direct_xmit declaration from sch_generic.h to pkt_sched.h 2. Update qdisc basic statistics for direct xmit path. 3. Set qlen to zero in qdisc_reset. 4. Changed some function names to more meaningful ones. Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/pkt_sched.h')
-rw-r--r--include/net/pkt_sched.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 82a3191375f..f911ec7598e 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -87,6 +87,9 @@ extern struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r,
extern void qdisc_put_rtab(struct qdisc_rate_table *tab);
extern void qdisc_put_stab(struct qdisc_size_table *tab);
extern void qdisc_warn_nonwc(char *txt, struct Qdisc *qdisc);
+extern int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
+ struct net_device *dev, struct netdev_queue *txq,
+ spinlock_t *root_lock);
extern void __qdisc_run(struct Qdisc *q);