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回复 5# mordorwww
退出napi轮询状态有以下三个条件：
1. 处理时间超期
2. budget用完
3. 网卡收到的包少于预期收到的包，每次poll的时候会指定收一定数量的包，如果这次poll得到的包个数小于这个值，就打开网卡中断，停止napi轮询
我刚的说法有误，无包的时候确实会停止，但如果持续有包，会一直poll到budget用完或超时
static void net_rx_action(struct softirq_action *h)
{
struct list_head *list = &__get_cpu_var(softnet_data).poll_list;
unsigned long time_limit = jiffies + 2;
int budget = netdev_budget;
void *have;
local_irq_disable();
while (!list_empty(list)) { /*在这儿死循环，网卡注册的poll函数里会调用napi_complete将其从pool_list里删除*/
struct napi_struct *n;
int work, weight;
/* If softirq window is exhuasted then punt.
* Allow this to run for 2 jiffies since which will allow
* an average latency of 1.5/HZ.
*/
if (unlikely(budget <= 0 || time_after(jiffies, time_limit)))/*这里判断是否超时或者用完budget，如果是，则poll结束*/
goto softnet_break;
local_irq_enable();
/* Even though interrupts have been re-enabled, this
* access is safe because interrupts can only add new
* entries to the tail of this list, and only ->poll()
* calls can remove this head entry from the list.
*/
n = list_first_entry(list, struct napi_struct, poll_list);
have = netpoll_poll_lock(n);
weight = n->weight;
/* This NAPI_STATE_SCHED test is for avoiding a race
* with netpoll's poll_napi(). Only the entity which
* obtains the lock and sees NAPI_STATE_SCHED set will
* actually make the ->poll() call. Therefore we avoid
* accidently calling ->poll() when NAPI is not scheduled.
*/
work = 0;
if (test_bit(NAPI_STATE_SCHED, &n->state)) {
work = n->poll(n, weight); /*这里调用网卡注册的poll函数进行收包*/
trace_napi_poll(n);
}
WARN_ON_ONCE(work > weight);
budget -= work; /* budget减去本次收到的包*/
local_irq_disable();
/* Drivers must not modify the NAPI state if they
* consume the entire weight. In such cases this code
* still "owns" the NAPI instance and therefore can
* move the instance around on the list at-will.
*/
if (unlikely(work == weight)) {
if (unlikely(napi_disable_pending(n))) {
local_irq_enable();
napi_complete(n);
local_irq_disable();
} else
list_move_tail(&n->poll_list, list);
}
netpoll_poll_unlock(have);
}
out:
local_irq_enable();
#ifdef CONFIG_NET_DMA
/*
* There may not be any more sk_buffs coming right now, so push
* any pending DMA copies to hardware
*/
dma_issue_pending_all();
#endif
return;
softnet_break:
__get_cpu_var(netdev_rx_stat).time_squeeze++;
__raise_softirq_irqoff(NET_RX_SOFTIRQ);
goto out;
}
以intel的82599网卡为例：
static int ixgbe_poll(struct napi_struct *napi, int budget)
{
struct ixgbe_q_vector *q_vector =
container_of(napi, struct ixgbe_q_vector, napi);
struct ixgbe_adapter *adapter = q_vector->adapter;
int tx_clean_complete, work_done = 0;
#ifdef CONFIG_IXGBE_DCA
if (adapter->flags & IXGBE_FLAG_DCA_ENABLED) {
ixgbe_update_tx_dca(adapter, adapter->tx_ring[0]);
ixgbe_update_rx_dca(adapter, adapter->rx_ring[0]);
}
#endif
tx_clean_complete = ixgbe_clean_tx_irq(q_vector, adapter->tx_ring[0]);
ixgbe_clean_rx_irq(q_vector, adapter->rx_ring[0], &work_done, budget);
if (!tx_clean_complete)
work_done = budget;
/* If budget not fully consumed, exit the polling mode */
if (work_done < budget) { /* 这里网卡如果没有收到预期的包个数，则会打开网卡中断，停止napi轮询 */
napi_complete(napi);
if (adapter->rx_itr_setting & 1)
ixgbe_set_itr(adapter);
if (!test_bit(__IXGBE_DOWN, &adapter->state))
ixgbe_irq_enable_queues(adapter, IXGBE_EIMS_RTX_QUEUE);
}
return work_done;
}
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发表于 2013-04-13 22:09
发表于 2013-04-14 10:33
