On Sun, Mar 15, 2015 at 02:50:27PM +0800, Linhaifeng wrote:
> Hi,Michael
>
> I had tested the start_xmit function by the follow code found that the tx
> queue's state is stopped and can't send any packets anymore.
Why don't you Cc all maintainers on this email?
Pls check the file MAINTAINERS for the full list.
I added Cc for now.
>
> static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> ... ...
>
>
> capacity = 10; //########## test code : force to call
> netif_stop_queue
>
> if (capacity < 2+MAX_SKB_FRAGS) {
> netif_stop_queue(dev);
So you changed code to make it think we are out of capacity, now it
stops the queue.
>
> if (unlikely(!virtqueue_enable_cb_delayed(vi->svq))) {
> /* More just got used, free them then recheck. */
> capacity += free_old_xmit_skbs(vi);
> dev_warn(&dev->dev, "free_old_xmit_skbs capacity =%d
> MAX_SKB_FRAGS=%d", capacity, MAX_SKB_FRAGS);
>
> capacity = 10; //########## test code
> : force not to call netif_start_queue
>
> if (capacity >= 2+MAX_SKB_FRAGS) {
> netif_start_queue(dev);
> virtqueue_disable_cb(vi->svq);
> } else {
> //########## OTOH if often enter this branch tx
> queue maybe stopped.
> }
and changed it here so it won't restart queue if host consumed
all buffers.
unsurprisingly this makes driver not work.
>
> }
>
> //########## Should we start queue here? I found that sometimes
> skb_xmit_done run before netif_stop_queue if this occurred the queue's state
> is
> //########## stopped and have to reload virtio-net module to
> restore network.
With or without your changes?
Is this the condition you describe?
if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
---> at this point, skb_xmit_done runs. this does:
/* Suppress further interrupts. */
virtqueue_disable_cb(vq);
/* We were probably waiting for more output buffers. */
netif_wake_subqueue(vi->dev, vq2txq(vq));
--->
netif_stop_subqueue(dev, qnum);
---> queue is now stopped
if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
----> this re-enables interrupts, after an interrupt skb_xmit_done
will run again.
/* More just got used, free them then recheck.
* */
free_old_xmit_skbs(sq);
if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
netif_start_subqueue(dev, qnum);
virtqueue_disable_cb(sq->vq);
}
}
}
I can't see a race condition from your description above.
> }
>
> }
>
> ping 9.62.1.2 -i 0.1
> 64 bytes from 9.62.1.2: icmp_seq=19 ttl=64 time=0.115 ms
> 64 bytes from 9.62.1.2: icmp_seq=20 ttl=64 time=0.101 ms
> 64 bytes from 9.62.1.2: icmp_seq=21 ttl=64 time=0.094 ms
> 64 bytes from 9.62.1.2: icmp_seq=22 ttl=64 time=0.098 ms
> 64 bytes from 9.62.1.2: icmp_seq=23 ttl=64 time=0.097 ms
> 64 bytes from 9.62.1.2: icmp_seq=24 ttl=64 time=0.095 ms
> 64 bytes from 9.62.1.2: icmp_seq=25 ttl=64 time=0.095 ms
> ....
> ping: sendmsg: No buffer space available
> ping: sendmsg: No buffer space available
> ping: sendmsg: No buffer space available
> ping: sendmsg: No buffer space available
> ping: sendmsg: No buffer space available
> ping: sendmsg: No buffer space available
> ....
>
> --
> Regards,
> Haifeng
I can't say what does your code-changing experiment show.
It might be better to introduce delay by calling something like
cpu_relax at specific points (maybe multiple times in a loop).
--
MST
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