93f154b594
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 <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
226 lines
5.5 KiB
C
226 lines
5.5 KiB
C
/*
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* INET An implementation of the TCP/IP protocol suite for the LINUX
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* operating system. INET is implemented using the BSD Socket
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* interface as the means of communication with the user level.
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*
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* Pseudo-driver for the loopback interface.
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*
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* Version: @(#)loopback.c 1.0.4b 08/16/93
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*
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* Authors: Ross Biro
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* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
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* Donald Becker, <becker@scyld.com>
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*
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* Alan Cox : Fixed oddments for NET3.014
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* Alan Cox : Rejig for NET3.029 snap #3
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* Alan Cox : Fixed NET3.029 bugs and sped up
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* Larry McVoy : Tiny tweak to double performance
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* Alan Cox : Backed out LMV's tweak - the linux mm
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* can't take it...
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* Michael Griffith: Don't bother computing the checksums
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* on packets received on the loopback
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* interface.
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* Alexey Kuznetsov: Potential hang under some extreme
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* cases removed.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/kernel.h>
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#include <linux/jiffies.h>
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#include <linux/module.h>
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#include <linux/interrupt.h>
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#include <linux/fs.h>
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/socket.h>
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#include <linux/errno.h>
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#include <linux/fcntl.h>
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#include <linux/in.h>
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#include <linux/init.h>
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#include <asm/system.h>
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#include <asm/uaccess.h>
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#include <asm/io.h>
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#include <linux/inet.h>
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#include <linux/netdevice.h>
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#include <linux/etherdevice.h>
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#include <linux/skbuff.h>
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#include <linux/ethtool.h>
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#include <net/sock.h>
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#include <net/checksum.h>
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#include <linux/if_ether.h> /* For the statistics structure. */
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#include <linux/if_arp.h> /* For ARPHRD_ETHER */
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#include <linux/ip.h>
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#include <linux/tcp.h>
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#include <linux/percpu.h>
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#include <net/net_namespace.h>
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struct pcpu_lstats {
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unsigned long packets;
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unsigned long bytes;
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unsigned long drops;
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};
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/*
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* The higher levels take care of making this non-reentrant (it's
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* called with bh's disabled).
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*/
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static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
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{
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struct pcpu_lstats *pcpu_lstats, *lb_stats;
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int len;
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skb_orphan(skb);
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skb->protocol = eth_type_trans(skb, dev);
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/* it's OK to use per_cpu_ptr() because BHs are off */
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pcpu_lstats = dev->ml_priv;
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lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());
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len = skb->len;
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if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
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lb_stats->bytes += len;
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lb_stats->packets++;
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} else
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lb_stats->drops++;
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return 0;
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}
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static struct net_device_stats *loopback_get_stats(struct net_device *dev)
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{
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const struct pcpu_lstats *pcpu_lstats;
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struct net_device_stats *stats = &dev->stats;
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unsigned long bytes = 0;
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unsigned long packets = 0;
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unsigned long drops = 0;
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int i;
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pcpu_lstats = dev->ml_priv;
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for_each_possible_cpu(i) {
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const struct pcpu_lstats *lb_stats;
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lb_stats = per_cpu_ptr(pcpu_lstats, i);
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bytes += lb_stats->bytes;
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packets += lb_stats->packets;
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drops += lb_stats->drops;
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}
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stats->rx_packets = packets;
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stats->tx_packets = packets;
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stats->rx_dropped = drops;
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stats->rx_errors = drops;
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stats->rx_bytes = bytes;
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stats->tx_bytes = bytes;
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return stats;
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}
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static u32 always_on(struct net_device *dev)
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{
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return 1;
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}
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static const struct ethtool_ops loopback_ethtool_ops = {
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.get_link = always_on,
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.set_tso = ethtool_op_set_tso,
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.get_tx_csum = always_on,
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.get_sg = always_on,
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.get_rx_csum = always_on,
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};
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static int loopback_dev_init(struct net_device *dev)
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{
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struct pcpu_lstats *lstats;
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lstats = alloc_percpu(struct pcpu_lstats);
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if (!lstats)
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return -ENOMEM;
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dev->ml_priv = lstats;
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return 0;
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}
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static void loopback_dev_free(struct net_device *dev)
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{
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struct pcpu_lstats *lstats = dev->ml_priv;
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free_percpu(lstats);
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free_netdev(dev);
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}
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static const struct net_device_ops loopback_ops = {
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.ndo_init = loopback_dev_init,
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.ndo_start_xmit= loopback_xmit,
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.ndo_get_stats = loopback_get_stats,
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};
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/*
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* The loopback device is special. There is only one instance
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* per network namespace.
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*/
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static void loopback_setup(struct net_device *dev)
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{
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dev->mtu = (16 * 1024) + 20 + 20 + 12;
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dev->hard_header_len = ETH_HLEN; /* 14 */
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dev->addr_len = ETH_ALEN; /* 6 */
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dev->tx_queue_len = 0;
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dev->type = ARPHRD_LOOPBACK; /* 0x0001*/
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dev->flags = IFF_LOOPBACK;
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dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
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dev->features = NETIF_F_SG | NETIF_F_FRAGLIST
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| NETIF_F_TSO
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| NETIF_F_NO_CSUM
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| NETIF_F_HIGHDMA
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| NETIF_F_LLTX
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| NETIF_F_NETNS_LOCAL;
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dev->ethtool_ops = &loopback_ethtool_ops;
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dev->header_ops = ð_header_ops;
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dev->netdev_ops = &loopback_ops;
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dev->destructor = loopback_dev_free;
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}
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/* Setup and register the loopback device. */
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static __net_init int loopback_net_init(struct net *net)
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{
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struct net_device *dev;
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int err;
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err = -ENOMEM;
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dev = alloc_netdev(0, "lo", loopback_setup);
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if (!dev)
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goto out;
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dev_net_set(dev, net);
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err = register_netdev(dev);
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if (err)
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goto out_free_netdev;
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net->loopback_dev = dev;
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return 0;
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out_free_netdev:
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free_netdev(dev);
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out:
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if (net == &init_net)
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panic("loopback: Failed to register netdevice: %d\n", err);
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return err;
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}
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static __net_exit void loopback_net_exit(struct net *net)
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{
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struct net_device *dev = net->loopback_dev;
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unregister_netdev(dev);
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}
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/* Registered in net/core/dev.c */
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struct pernet_operations __net_initdata loopback_net_ops = {
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.init = loopback_net_init,
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.exit = loopback_net_exit,
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};
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