Messages in this thread |  | | Date | Thu, 10 Jan 2013 17:26:22 +0800 | From | Wanlong Gao <> | Subject | Re: [PATCH V3 1/2] virtio-net: fix the set affinity bug when CPU IDs are not consecutive |
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On 01/10/2013 08:49 AM, Rusty Russell wrote: > Wanlong Gao <gaowanlong@cn.fujitsu.com> writes: >> On 01/09/2013 07:31 AM, Rusty Russell wrote: >>> 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; >>> } >> >> Got it, thank you. >> >>> >>> Now, just to confirm, I assume this can happen even if we use vq_index, >>> right, because of races with virtnet_set_channels? >> >> I still can't understand this race, could you explain more? thank you. > > I assume that someone can call virtnet_set_channels() while we are > inside virtnet_select_queue(), so they reduce dev->real_num_tx_queues, > causing virtnet_set_channels to do: > > while (unlikely(txq >= dev->real_num_tx_queues)) > txq -= dev->real_num_tx_queues; > > Otherwise, when is this loop called?
How about just remove this loop?
Eric, can you give a help here?
Thanks, Wanlong Gao
> > Thanks, > Rusty. >
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