Re: [PATCH V3 1/2] virtio-net: fix the set affinity bug when CPU IDs are not consecutive

Rusty Russell
2013-01-08T23:43:53Z

Wanlong Gao <gaowanlong@cn.fujitsu.com> writes:
> */
> static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
> {
> - int txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
> - smp_processor_id();
> + int txq = 0;
> +
> + if (skb_rx_queue_recorded(skb))
> + txq = skb_get_rx_queue(skb);
> + else if ((txq = per_cpu(vq_index, smp_processor_id())) == -1)
> + txq = 0;

You should use __get_cpu_var() instead of smp_processor_id() here, ie:

else if ((txq = __get_cpu_var(vq_index)) == -1)

And AFAICT, no reason to initialize txq to 0 to start with.

So:

int txq;

if (skb_rx_queue_recorded(skb))
txq = skb_get_rx_queue(skb);
else {
txq = __get_cpu_var(vq_index);
if (txq == -1)
txq = 0;
}

Now, just to confirm, I assume this can happen even if we use vq_index,
right, because of races with virtnet_set_channels?

while (unlikely(txq >= dev->real_num_tx_queues))
txq -= dev->real_num_tx_queues;

Thanks,
Rusty.