From 8236632fb3532188c75656421e29f5ab51b47db7 Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Tue, 25 Sep 2007 19:27:13 -0700 Subject: [PATCH] [NET_SCHED]: explict hold dev tx lock For N cpus, with full throttle traffic on all N CPUs, funneling traffic to the same ethernet device, the devices queue lock is contended by all N CPUs constantly. The TX lock is only contended by a max of 2 CPUS. In the current mode of operation, after all the work of entering the dequeue region, we may endup aborting the path if we are unable to get the tx lock and go back to contend for the queue lock. As N goes up, this gets worse. The changes in this patch result in a small increase in performance with a 4CPU (2xdual-core) with no irq binding. Both e1000 and tg3 showed similar behavior; Signed-off-by: Jamal Hadi Salim Signed-off-by: David S. Miller --- net/sched/sch_generic.c | 19 ++----------------- 1 file changed, 2 insertions(+), 17 deletions(-) diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index e970e8e..95ae119 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -134,34 +134,19 @@ static inline int qdisc_restart(struct net_device *dev) { struct Qdisc *q = dev->qdisc; struct sk_buff *skb; - unsigned lockless; int ret; /* Dequeue packet */ if (unlikely((skb = dev_dequeue_skb(dev, q)) == NULL)) return 0; - /* - * When the driver has LLTX set, it does its own locking in - * start_xmit. These checks are worth it because even uncongested - * locks can be quite expensive. The driver can do a trylock, as - * is being done here; in case of lock contention it should return - * NETDEV_TX_LOCKED and the packet will be requeued. - */ - lockless = (dev->features & NETIF_F_LLTX); - - if (!lockless && !netif_tx_trylock(dev)) { - /* Another CPU grabbed the driver tx lock */ - return handle_dev_cpu_collision(skb, dev, q); - } /* And release queue */ spin_unlock(&dev->queue_lock); + HARD_TX_LOCK(dev, smp_processor_id()); ret = dev_hard_start_xmit(skb, dev); - - if (!lockless) - netif_tx_unlock(dev); + HARD_TX_UNLOCK(dev); spin_lock(&dev->queue_lock); q = dev->qdisc; -- 2.7.4