Linux内核中RPS/RFS代码分析
netdev_rx_queue表示对应的接收队列，不少网卡硬件上已经支持多个队列，此时就会有多个netdev_rx_queue队列，这个结构是挂在net_device，初始化接收队列的函数：netif_alloc_rx_queuesapi
netif_alloc_rx_queues
数组
static int netif_alloc_rx_queues(struct net_device *dev)
{
/*获取接收队列的个数*/
unsigned int i, count = netdev_extended(dev)->rps_data.num_rx_queues;
struct netdev_rx_queue *rx;
BUG_ON(count < 1);
/*分配netdev_rx_queue 空间*/
rx = kcalloc(count, sizeof(struct netdev_rx_queue), GFP_KERNEL);
if (!rx) {
pr_err("netdev: Unable to allocate %u rx queues.\n", count);
return -ENOMEM;
}
/* netdev_rx_queue 和net_device关联起来。*/
netdev_extended(dev)->rps_data._rx = rx;
/*对netdev_rx_queue 中net_device进行赋值操做*/
for (i = 0; i < count; i++)
rx[i].dev = dev;
return 0;
}
struct netdev_rx_queue {
/*保存当前队列的rps map*/
struct rps_map *rps_map;
/* //每一个设备的队列保存了一个rps_dev_flow_table */
struct rps_dev_flow_table *rps_flow_table;
//对应的kobject
struct kobject kobj;
/*所属的net_device*/
struct net_device *dev;
} ____cacheline_aligned_in_smp;
struct rps_map {
/*CPU的个数，也就是CPU数组的个数*/
unsigned int len;
struct rcu_head rcu;
/*保存了CPU的ID*/
u16 cpus[0];
};
get_rps_cpu
static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
struct rps_dev_flow **rflowp)
{
struct ipv6hdr *ip6;
struct iphdr *ip;
struct netdev_rx_queue *rxqueue;
struct rps_map *map;
struct rps_dev_flow_table *flow_table;
struct rps_sock_flow_table *sock_flow_table;
struct netdev_rps_info *rpinfo = &netdev_extended(dev)->rps_data;
int cpu = -1;
int tcpu;
u8 ip_proto;
u32 addr1, addr2, ports, ihl;
rcu_read_lock();
if (skb_rx_queue_recorded(skb)) {
/*获取设备对应的rx队列。*/
u16 index = skb_get_rx_queue(skb);
if (unlikely(index >= rpinfo->num_rx_queues)) {
WARN_ONCE(rpinfo->num_rx_queues > 1, "%s received packet "
"on queue %u, but number of RX queues is %u\n",
dev->name, index, rpinfo->num_rx_queues);
goto done;
}
rxqueue = rpinfo->_rx + index;
} else
rxqueue = rpinfo->_rx;
if (!rxqueue->rps_map && !rxqueue->rps_flow_table)
goto done;
if (skb->rxhash) //若是硬件已经计算过，则直接跳过，不须要计算HASH值
goto got_hash; /* Skip hash computation on packet header */
switch (skb->protocol) { /*根据不一样的IP协议获取源IP和目的IP*/
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))); /*获取四层协议的端口号，tcp头的前4个字节就是源和目的端口，所以这里跳过ip头获得tcp头的前4个字节*/
break;
default:
break;
}
/*根据获取到的SIP和DIP，PORT计算HSAH值，*/
skb->rxhash = jhash_3words(addr1, addr2, ports, hashrnd) >> 16;
if (!skb->rxhash)
skb->rxhash = 1;
got_hash:
/* rps_sock_flow_table和rps_dev_flow_table 是为了解决RFS而添加的两张表，rps_sock_flow_table是一个全局的hash表，这个表针对socket的，映射了socket对应的cpu，这里的cpu就是应用层期待软中断所在的cpu ，rps_dev_flow_table,这个是针对设备的，每一个设备队列都含有一个rps_dev_flow_table(这个表主要是保存了上次处理相同连接上的skb所在的cpu),这个hash表中每个元素包含了一个cpu id，一个tail queue的计数器*/
flow_table = rcu_dereference(rxqueue->rps_flow_table);
sock_flow_table = rcu_dereference(rps_sock_flow_table);
if (flow_table && sock_flow_table) {
u16 next_cpu;
struct rps_dev_flow *rflow;
rflow = &flow_table->flows[skb->rxhash & flow_table->mask];
tcpu = rflow->cpu;
next_cpu = sock_flow_table->ents[skb->rxhash &
sock_flow_table->mask];
/*首先会获得两个flow table，一个是sock_flow_table,另外一个是设备的rps_flow_table(skb对应的设备队列中对应的flow table)，这里的逻辑是这样子的取出来两个cpu，一个是根据rps计算数据包前一次被调度过的cpu(tcpu)，一个是应用程序指望的cpu(next_cpu)，而后比较这两个值，若是 1 tcpu未设置(等于RPS_NO_CPU） 2 tcpu是离线的 3 tcpu的input_queue_head大于rps_flow_table中的last_qtail 的话就调度这个skb到next_cpu.而这里第三点input_queue_head大于rps_flow_table则说明在当前的dev flow table中的数据包已经发送完毕，不然的话为了不乱序就仍是继续使用tcpu
* If the desired CPU (where last recvmsg was done) is
* different from current CPU (one in the rx-queue flow
* table entry), switch if one of the following holds:
* - Current CPU is unset (equal to RPS_NO_CPU).
* - Current CPU is offline.
* - The current CPU's queue tail has advanced beyond the
* last packet that was enqueued using this table entry.
* This guarantees that all previous packets for the flow
* have been dequeued, thus preserving in order delivery.
*/
if (unlikely(tcpu != next_cpu) &&
(tcpu == RPS_NO_CPU || !cpu_online(tcpu) ||
((int)(per_cpu(softnet_data, tcpu).input_queue_head -
rflow->last_qtail)) >= 0)) {
tcpu = rflow->cpu = next_cpu;
if (tcpu != RPS_NO_CPU)
rflow->last_qtail = per_cpu(softnet_data,
tcpu).input_queue_head;
}
if (tcpu != RPS_NO_CPU && cpu_online(tcpu)) {
*rflowp = rflow;
/*设置返回的CPU*/
cpu = tcpu;
goto done;
}
}
/*当第一次进来时tcpu是RPS_NO_CPU,而且next_cpu也是RPS_NO_CPU，此时会致使跳过rfs处理，而是直接使用rps的处理, */
map = rcu_dereference(rxqueue->rps_map);
if (map) {
tcpu = map->cpus[((u32) (skb->rxhash * map->len)) >> 16];
/*若是cpu是online的，则返回计算出的这个cpu */
if (cpu_online(tcpu)) {
cpu = tcpu;
goto done;
}
}
done:
rcu_read_unlock();
return cpu;
}
/*将skb挂在到对应cpu的input queue上的, enqueue_to_backlog接受一个skb和cpu为参数，经过cpu来判断skb如何处理。要么加入所属的input_pkt_queue中，要么schecule 软中断*/
enqueue_to_backlog
static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
unsigned int *qtail)
{
struct softnet_data *queue;
unsigned long flags;
/*根据传递过来的CPU，获取softnet_data结构体*/
queue = &per_cpu(softnet_data, cpu);
local_irq_save(flags);
__get_cpu_var(netdev_rx_stat).total++;
spin_lock(&queue->input_pkt_queue.lock);
if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
if (queue->input_pkt_queue.qlen) {
enqueue:/*将数据包添加到input_pkt_queue队列中*/
__skb_queue_tail(&queue->input_pkt_queue, skb);
*qtail = queue->input_queue_head +
queue->input_pkt_queue.qlen;
spin_unlock_irqrestore(&queue->input_pkt_queue.lock,
flags);
return NET_RX_SUCCESS;
}
/* Schedule NAPI for backlog device 能够调度软中断*/
if (napi_schedule_prep(&queue->backlog)) {
if (cpu != smp_processor_id()) {/*判断该SKB是否该CPU处理*/
struct rps_remote_softirq_cpus *rcpus =
&__get_cpu_var(rps_remote_softirq_cpus);
cpu_set(cpu, rcpus->mask[rcpus->select]);
__raise_softirq_irqoff(NET_RX_SOFTIRQ);
} else
/*应该当前cpu处理，则直接schedule 软中断，这里能够看到传递进去的是backlog */
____napi_schedule(queue, &queue->backlog);
}
goto enqueue;
}
spin_unlock(&queue->input_pkt_queue.lock);
__get_cpu_var(netdev_rx_stat).dropped++;
local_irq_restore(flags);
kfree_skb(skb);
return NET_RX_DROP;
}
enqueue_to_backlog
static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
unsigned int *qtail)
{
struct softnet_data *queue;
unsigned long flags;
/*根据传递过来的CPU，获取softnet_data结构体*/
queue = &per_cpu(softnet_data, cpu);
local_irq_save(flags);
__get_cpu_var(netdev_rx_stat).total++;
spin_lock(&queue->input_pkt_queue.lock);
if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
if (queue->input_pkt_queue.qlen) {
enqueue:/*将数据包添加到input_pkt_queue队列中*/
__skb_queue_tail(&queue->input_pkt_queue, skb);
*qtail = queue->input_queue_head +
queue->input_pkt_queue.qlen;
spin_unlock_irqrestore(&queue->input_pkt_queue.lock,
flags);
return NET_RX_SUCCESS;
}
/* Schedule NAPI for backlog device 能够调度软中断*/
if (napi_schedule_prep(&queue->backlog)) {
if (cpu != smp_processor_id()) {/*判断该SKB是否该CPU处理*/
struct rps_remote_softirq_cpus *rcpus =
&__get_cpu_var(rps_remote_softirq_cpus);
cpu_set(cpu, rcpus->mask[rcpus->select]);
__raise_softirq_irqoff(NET_RX_SOFTIRQ);
} else
/*应该当前cpu处理，则直接schedule 软中断，这里能够看到传递进去的是backlog */
____napi_schedule(queue, &queue->backlog);
}
goto enqueue;
}
spin_unlock(&queue->input_pkt_queue.lock);
__get_cpu_var(netdev_rx_stat).dropped++;
local_irq_restore(flags);
kfree_skb(skb);
return NET_RX_DROP;
}
inet_recvmsg
int inet_recvmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
size_t size, int flags)
{
struct sock *sk = sock->sk;
int addr_len = 0;
int err;
inet_rps_record_flow(sk);//设置HASH表
err = sk->sk_prot->recvmsg(iocb, sk, msg, size, flags & MSG_DONTWAIT,
flags & ~MSG_DONTWAIT, &addr_len);
if (err >= 0)
msg->msg_namelen = addr_len;
return err;
}
这个函数主要是获得全局的rps_sock_flow_table，而后调用rps_record_sock_flow来对rps_sock_flow_table进行设置，这里会将socket的sk_rxhash传递进去看成hash的索引，而这个sk_rxhash其实就是skb里面的rxhash，skb的rxhash就是rps中设置的hash值，这个值是根据四元组进行hash的。这里用这个当索引一个是为了相同的socket都能落入一个index。并且下面的软中断上下文也比较容易存取这个hash表socket
inet_rps_record_flow
点击(此处)折叠或打开tcp
static inline void inet_rps_record_flow(struct sock *sk)
{
struct rps_sock_flow_table *sock_flow_table;
rcu_read_lock();
sock_flow_table = rcu_dereference(rps_sock_flow_table);
rps_record_sock_flow(sock_flow_table, inet_sk_rxhash(sk));
rcu_read_unlock();
}
rps_record_sock_flow
点击(此处)折叠或打开函数
static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
u32 hash)
{
if (table && hash) {
/*获取索引*/
unsigned int cpu, index = hash & table->mask;
/* We only give a hint, preemption can change cpu under us 获取CPU */
cpu = raw_smp_processor_id();
/*保存对应的cpu,若是等于当前cpu，则说明已经设置过了*/
if (table->ents[index] != cpu)
table->ents[index] = cpu;
}
}
图：内核代码流程this
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