From 93f154b594fe47e4a7e5358b309add449a046cd3 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 18 May 2009 22:19:19 -0700 Subject: [PATCH] net: release dst entry in dev_hard_start_xmit() One point of contention in high network loads is the dst_release() performed when a transmited skb is freed. This is because NIC tx completion calls dev_kree_skb() long after original call to dev_queue_xmit(skb). CPU cache is cold and the atomic op in dst_release() stalls. On SMP, this is quite visible if one CPU is 100% handling softirqs for a network device, since dst_clone() is done by other cpus, involving cache line ping pongs. It seems right place to release dst is in dev_hard_start_xmit(), for most devices but ones that are virtual, and some exceptions. David Miller suggested to define a new device flag, set in alloc_netdev_mq() (so that most devices set it at init time), and carefuly unset in devices which dont want a NULL skb->dst in their ndo_start_xmit(). List of devices that must clear this flag is : - loopback device, because it calls netif_rx() and quoting Patrick : "ip_route_input() doesn't accept loopback addresses, so loopback packets already need to have a dst_entry attached." - appletalk/ipddp.c : needs skb->dst in its xmit function - And all devices that call again dev_queue_xmit() from their xmit function (as some classifiers need skb->dst) : bonding, vlan, macvlan, eql, ifb, hdlc_fr Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- drivers/net/appletalk/ipddp.c | 1 + drivers/net/bonding/bond_main.c | 1 + drivers/net/eql.c | 1 + drivers/net/ifb.c | 1 + drivers/net/loopback.c | 1 + drivers/net/macvlan.c | 1 + drivers/net/wan/hdlc_fr.c | 1 + include/linux/if.h | 3 +++ net/8021q/vlan_dev.c | 1 + net/core/dev.c | 9 +++++++++ 10 files changed, 20 insertions(+) diff --git a/drivers/net/appletalk/ipddp.c b/drivers/net/appletalk/ipddp.c index da64ba88d7f8..f939e92fcf8a 100644 --- a/drivers/net/appletalk/ipddp.c +++ b/drivers/net/appletalk/ipddp.c @@ -71,6 +71,7 @@ static struct net_device * __init ipddp_init(void) if (!dev) return ERR_PTR(-ENOMEM); + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; strcpy(dev->name, "ipddp%d"); if (version_printed++ == 0) diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 96d7689995cd..92a9d69c5650 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -5148,6 +5148,7 @@ int bond_create(char *name, struct bond_params *params) goto out_rtnl; } + bond_dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; if (!name) { res = dev_alloc_name(bond_dev, "bond%d"); if (res < 0) diff --git a/drivers/net/eql.c b/drivers/net/eql.c index 5210bb1027cc..19b7dd983944 100644 --- a/drivers/net/eql.c +++ b/drivers/net/eql.c @@ -194,6 +194,7 @@ static void __init eql_setup(struct net_device *dev) dev->type = ARPHRD_SLIP; dev->tx_queue_len = 5; /* Hands them off fast */ + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; } static int eql_open(struct net_device *dev) diff --git a/drivers/net/ifb.c b/drivers/net/ifb.c index 60a263001933..96713ef06298 100644 --- a/drivers/net/ifb.c +++ b/drivers/net/ifb.c @@ -156,6 +156,7 @@ static void ifb_setup(struct net_device *dev) dev->flags |= IFF_NOARP; dev->flags &= ~IFF_MULTICAST; + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; random_ether_addr(dev->dev_addr); } diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c index 6f71157bea8e..da472c687481 100644 --- a/drivers/net/loopback.c +++ b/drivers/net/loopback.c @@ -170,6 +170,7 @@ static void loopback_setup(struct net_device *dev) dev->tx_queue_len = 0; dev->type = ARPHRD_LOOPBACK; /* 0x0001*/ dev->flags = IFF_LOOPBACK; + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; dev->features = NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO | NETIF_F_NO_CSUM diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c index 329cd50d0e29..d5334b41e4b4 100644 --- a/drivers/net/macvlan.c +++ b/drivers/net/macvlan.c @@ -414,6 +414,7 @@ static void macvlan_setup(struct net_device *dev) { ether_setup(dev); + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; dev->netdev_ops = &macvlan_netdev_ops; dev->destructor = free_netdev; dev->header_ops = &macvlan_hard_header_ops, diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c index 800530101093..bfa0161a02d3 100644 --- a/drivers/net/wan/hdlc_fr.c +++ b/drivers/net/wan/hdlc_fr.c @@ -1054,6 +1054,7 @@ static void pvc_setup(struct net_device *dev) dev->flags = IFF_POINTOPOINT; dev->hard_header_len = 10; dev->addr_len = 2; + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; } static const struct net_device_ops pvc_ops = { diff --git a/include/linux/if.h b/include/linux/if.h index 1108f3e099e3..b9a6229f3be7 100644 --- a/include/linux/if.h +++ b/include/linux/if.h @@ -67,6 +67,9 @@ #define IFF_ISATAP 0x80 /* ISATAP interface (RFC4214) */ #define IFF_MASTER_ARPMON 0x100 /* bonding master, ARP mon in use */ #define IFF_WAN_HDLC 0x200 /* WAN HDLC device */ +#define IFF_XMIT_DST_RELEASE 0x400 /* dev_hard_start_xmit() is allowed to + * release skb->dst + */ #define IF_GET_IFACE 0x0001 /* for querying only */ #define IF_GET_PROTO 0x0002 diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index 8faacee68633..ff7572ac5481 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -739,6 +739,7 @@ void vlan_setup(struct net_device *dev) ether_setup(dev); dev->priv_flags |= IFF_802_1Q_VLAN; + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; dev->tx_queue_len = 0; dev->netdev_ops = &vlan_netdev_ops; diff --git a/net/core/dev.c b/net/core/dev.c index 6d3630d16271..92ebeca29901 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -1688,6 +1688,14 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, goto gso; } + /* + * If device doesnt need skb->dst, release it right now while + * its hot in this cpu cache + */ + if ((dev->priv_flags & IFF_XMIT_DST_RELEASE) && skb->dst) { + dst_release(skb->dst); + skb->dst = NULL; + } rc = ops->ndo_start_xmit(skb, dev); /* * TODO: if skb_orphan() was called by @@ -5045,6 +5053,7 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name, netdev_init_queues(dev); INIT_LIST_HEAD(&dev->napi_list); + dev->priv_flags = IFF_XMIT_DST_RELEASE; setup(dev); strcpy(dev->name, name); return dev;