Commit 73d0d56a authored by Andi Kleen's avatar Andi Kleen Committed by David S. Miller

[NET]: NETIF_F_LLTX for devices

New version of the NETIF_F_LLTX for network devices patch. 

This allows network drivers to set the NETIF_F_LLTX flag
and then do their own locking in start_queue_xmit. 
This lowers locking overhead in this critical path. 

The drivers can use try lock if they want and return -1
when the lock wasn't grabbed. In this case the packet
will be requeued. For better compatibility this is only
done for drivers with LLTX set, others don't give a special
meaning to -1.

Most of the modern drivers who have a lock around hard_start_xmit
can just set this flag. It may be a good idea to convert the spin
lock there to a try lock. The only thing that should be audited
is that they do enough locking in the set_multicast_list function
too, and not also rely on xmit_lock here.

Now doesn't move any code around and does things with gotos instead.

The loop printk is also still there even for NETIF_F_LLTX

For drivers that don't set the new flag nothing changes.
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fb4a020e
......@@ -634,7 +634,8 @@ static void inject(struct pktgen_info* info)
nr_frags = skb_shinfo(skb)->nr_frags;
spin_lock_bh(&odev->xmit_lock);
if (!(odev->features & NETIF_F_LLTX))
spin_lock_bh(&odev->xmit_lock);
if (!netif_queue_stopped(odev)) {
atomic_inc(&skb->users);
......@@ -659,8 +660,8 @@ static void inject(struct pktgen_info* info)
last_ok = 0;
}
spin_unlock_bh(&odev->xmit_lock);
if (!(odev->features & NETIF_F_LLTX))
spin_unlock_bh(&odev->xmit_lock);
if (info->ipg) {
/* Try not to busy-spin if we have larger sleep times.
......
......@@ -97,46 +97,73 @@ int qdisc_restart(struct net_device *dev)
/* Dequeue packet */
if ((skb = q->dequeue(q)) != NULL) {
if (spin_trylock(&dev->xmit_lock)) {
unsigned nolock = (dev->features & NETIF_F_LLTX);
/*
* When the driver has LLTX set it does its own locking
* in start_xmit. No need to add additional overhead by
* locking again. These checks are worth it because
* even uncongested locks can be quite expensive.
* The driver can do trylock like here too, in case
* of lock congestion it should return -1 and the packet
* will be requeued.
*/
if (!nolock) {
if (!spin_trylock(&dev->xmit_lock)) {
collision:
/* So, someone grabbed the driver. */
/* It may be transient configuration error,
when hard_start_xmit() recurses. We detect
it by checking xmit owner and drop the
packet when deadloop is detected.
*/
if (dev->xmit_lock_owner == smp_processor_id()) {
kfree_skb(skb);
if (net_ratelimit())
printk(KERN_DEBUG "Dead loop on netdevice %s, fix it urgently!\n", dev->name);
return -1;
}
__get_cpu_var(netdev_rx_stat).cpu_collision++;
goto requeue;
}
/* Remember that the driver is grabbed by us. */
dev->xmit_lock_owner = smp_processor_id();
}
{
/* And release queue */
spin_unlock(&dev->queue_lock);
if (!netif_queue_stopped(dev)) {
int ret;
if (netdev_nit)
dev_queue_xmit_nit(skb, dev);
if (dev->hard_start_xmit(skb, dev) == 0) {
dev->xmit_lock_owner = -1;
spin_unlock(&dev->xmit_lock);
/* hard_start_xmit returns:
0 device not ready
1 everything ok
-1 didn't get device lock (for LLTX)
*/
ret = dev->hard_start_xmit(skb, dev);
if (ret == 0) {
if (!nolock) {
dev->xmit_lock_owner = -1;
spin_unlock(&dev->xmit_lock);
}
spin_lock(&dev->queue_lock);
return -1;
}
if (ret == -1 && nolock)
goto collision;
}
/* Release the driver */
dev->xmit_lock_owner = -1;
spin_unlock(&dev->xmit_lock);
if (!nolock) {
dev->xmit_lock_owner = -1;
spin_unlock(&dev->xmit_lock);
}
spin_lock(&dev->queue_lock);
q = dev->qdisc;
} else {
/* So, someone grabbed the driver. */
/* It may be transient configuration error,
when hard_start_xmit() recurses. We detect
it by checking xmit owner and drop the
packet when deadloop is detected.
*/
if (dev->xmit_lock_owner == smp_processor_id()) {
kfree_skb(skb);
if (net_ratelimit())
printk(KERN_DEBUG "Dead loop on netdevice %s, fix it urgently!\n", dev->name);
return -1;
}
__get_cpu_var(netdev_rx_stat).cpu_collision++;
}
/* Device kicked us out :(
......@@ -149,6 +176,7 @@ int qdisc_restart(struct net_device *dev)
3. device is buggy (ppp)
*/
requeue:
q->ops->requeue(skb, q);
netif_schedule(dev);
return 1;
......
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