- 论坛徽章:
- 0
|
它是否可以保证相同的 connection 分配在相同的 CPU 上？如果不能保证，那么是否可能会产生乱序现象？
platinum 发表于 2010-07-21 09:59 
不会乱序，使用对skb进行hash的方法，保证了不会乱序，不过，作者说样会导致CPU 缓存不命中，带来一定的性能形销，解决方法是，同时支持硬件hash，以达到加速的目的。（我现在还没有搞懂，网卡如何利用之）。
以下代码是计算hash并找到与之对应的CPU:- +static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb)
- +{
- + struct ipv6hdr *ip6;
- + struct iphdr *ip;
- + struct netdev_rx_queue *rxqueue;
- + struct rps_map *map;
- + int cpu = -1;
- + u8 ip_proto;
- + u32 addr1, addr2, ports, ihl;
- +
- + rcu_read_lock();
- +
- + if (skb_rx_queue_recorded(skb)) {
- + u16 index = skb_get_rx_queue(skb);
- + if (unlikely(index >= dev->num_rx_queues)) {
- + if (net_ratelimit()) {
- + WARN(1, "Received packet on %s for queue %u, "
- + "but number of RX queues is %u\n",
- + dev->name, index, dev->num_rx_queues);
- + }
- + goto done;
- + }
- + rxqueue = dev->_rx + index;
- + } else
- + rxqueue = dev->_rx;
- +
- + if (!rxqueue->rps_map)
- + goto done;
- +
- + if (skb->rxhash)
- + goto got_hash; /* Skip hash computation on packet header */
- +
- + switch (skb->protocol) {
- + case __constant_htons(ETH_P_IP):
- + if (!pskb_may_pull(skb, sizeof(*ip)))
- + goto done;
- +
- + ip = (struct iphdr *) skb->data;
- + ip_proto = ip->protocol;
- + addr1 = ip->saddr;
- + addr2 = ip->daddr;
- + ihl = ip->ihl;
- + break;
- + case __constant_htons(ETH_P_IPV6):
- + if (!pskb_may_pull(skb, sizeof(*ip6)))
- + goto done;
- +
- + ip6 = (struct ipv6hdr *) skb->data;
- + ip_proto = ip6->nexthdr;
- + addr1 = ip6->saddr.s6_addr32[3];
- + addr2 = ip6->daddr.s6_addr32[3];
- + ihl = (40 >> 2);
- + break;
- + default:
- + goto done;
- + }
- + ports = 0;
- + switch (ip_proto) {
- + case IPPROTO_TCP:
- + case IPPROTO_UDP:
- + case IPPROTO_DCCP:
- + case IPPROTO_ESP:
- + case IPPROTO_AH:
- + case IPPROTO_SCTP:
- + case IPPROTO_UDPLITE:
- + if (pskb_may_pull(skb, (ihl * 4) + 4))
- + ports = *((u32 *) (skb->data + (ihl * 4)));
- + break;
- +
- + default:
- + break;
- + }
- +
- + skb->rxhash = jhash_3words(addr1, addr2, ports, hashrnd);
- + if (!skb->rxhash)
- + skb->rxhash = 1;
- +
- +got_hash:
- + map = rcu_dereference(rxqueue->rps_map);
- + if (map) {
- + u16 tcpu = map->cpus[((u64) skb->rxhash * map->len) >> 32];
- +
- + if (cpu_online(tcpu)) {
- + cpu = tcpu;
- + goto done;
- + }
- + }
- +
- +done:
- + rcu_read_unlock();
- + return cpu;
- +}
|
|
免费注册
楼主: 瀚海书香
发表于 2010-07-21 09:59
发表于 2010-07-21 10:10
发表于 2010-07-21 10:13
