netdev - Re: [PATCH V7 1/3] virtio-net: fix the set affinity bug when CPU IDs are not consecutive

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Date:	Fri, 25 Jan 2013 17:16:14 +0800
From:	Wanlong Gao <gaowanlong@...fujitsu.com>
To:	Jason Wang <jasowang@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Eric Dumazet <erdnetdev@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	Wanlong Gao <gaowanlong@...fujitsu.com>
Subject: Re: [PATCH V7 1/3] virtio-net: fix the set affinity bug when CPU
 IDs are not consecutive


>>>>  
>>>> -	for (i = 0; i < vi->max_queue_pairs; i++) {
>>>> -		int cpu = set ? i : -1;
>>>> -		virtqueue_set_affinity(vi->rq[i].vq, cpu);
>>>> -		virtqueue_set_affinity(vi->sq[i].vq, cpu);
>>>> -	}
>>>> +	if (set) {
>>>> +		i = 0;
>>>> +		for_each_online_cpu(cpu) {
>>>> +			virtqueue_set_affinity(vi->rq[i].vq, cpu);
>>>> +			virtqueue_set_affinity(vi->sq[i].vq, cpu);
>>>> +			*per_cpu_ptr(vi->vq_index, cpu) = i;
>>>> +			i++;
>>>> +		}
>>>>  
>>>> -	if (set)
>>>>  		vi->affinity_hint_set = true;
>>>> -	else
>>>> +	} else {
>>>> +		for(i = 0; i < vi->max_queue_pairs; i++) {
>>>> +			virtqueue_set_affinity(vi->rq[i].vq, -1);
>>>> +			virtqueue_set_affinity(vi->sq[i].vq, -1);
>>>> +		}
>>>> +
>>>> +		i = 0;
>>>> +		for_each_online_cpu(cpu)
>>>> +			*per_cpu_ptr(vi->vq_index, cpu) =
>>>> +				++i % vi->curr_queue_pairs;
>>>> +
>>>>  		vi->affinity_hint_set = false;
>>>> +	}
>>>>  }
>>> Sorry, looks like the issue of v6 still exists, we need set per-cpu
>>> index unconditionally here (and also in 2/3), the cpus != queues check
>>> may bypass this setting.
>> This fixed in 2/3, when cpus != queues, it will go into virtnet_clean_affinity(in 2/3),
>> then vq index is set in virtnet_clean_affinity. Am I missing something?
> 
> Ah, so 2/3 looks fine. I suggest to fix this in 1/3 since it's not good
> to introduce a bug in patch 1 and fix it in patch 2, and this can also
> confuse the bisect.
> 

Make sense, will move the fix from 2/3 to 1/3.

Thanks,
Wanlong Gao

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