Subject: Re: [PATCH net-next] virtio-net: switch to use XPS to choose txq

From: Jason Wang <[email-masked]>
Date: Mon, 30 Sep 2013 11:20:00 +0800

On 09/30/2013 07:35 AM, Rusty Russell wrote:
> Jason Wang <[email-masked]> writes:
>> We used to use a percpu structure vq_index to record the cpu to queue
>> mapping, this is suboptimal since it duplicates the work of XPS and
>> loses all other XPS functionality such as allowing use to configure
>> their own transmission steering strategy.
>>
>> So this patch switches to use XPS and suggest a default mapping when
>> the number of cpus is equal to the number of queues. With XPS support,
>> there's no need for keeping per-cpu vq_index and .ndo_select_queue(),
>> so they were removed also.
>>
>> Cc: Rusty Russell <[email-masked]>
>> Cc: Michael S. Tsirkin <[email-masked]>
>> Signed-off-by: Jason Wang <[email-masked]>
>> ---
>>  drivers/net/virtio_net.c |   55 +++++++--------------------------------------
>>  1 files changed, 9 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index defec2b..4102c1b 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -127,9 +127,6 @@ struct virtnet_info {
>>  	/* Does the affinity hint is set for virtqueues? */
>>  	bool affinity_hint_set;
>>  
>> -	/* Per-cpu variable to show the mapping from CPU to virtqueue */
>> -	int __percpu *vq_index;
>> -
>>  	/* CPU hot plug notifier */
>>  	struct notifier_block nb;
>>  };
>> @@ -1063,7 +1060,6 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev,
>>  static void virtnet_clean_affinity(struct virtnet_info *vi, long hcpu)
>>  {
>>  	int i;
>> -	int cpu;
>>  
>>  	if (vi->affinity_hint_set) {
>>  		for (i = 0; i < vi->max_queue_pairs; i++) {
>> @@ -1073,20 +1069,11 @@ static void virtnet_clean_affinity(struct virtnet_info *vi, long hcpu)
>>  
>>  		vi->affinity_hint_set = false;
>>  	}
>> -
>> -	i = 0;
>> -	for_each_online_cpu(cpu) {
>> -		if (cpu == hcpu) {
>> -			*per_cpu_ptr(vi->vq_index, cpu) = -1;
>> -		} else {
>> -			*per_cpu_ptr(vi->vq_index, cpu) =
>> -				++i % vi->curr_queue_pairs;
>> -		}
>> -	}
>>  }
>>  
>>  static void virtnet_set_affinity(struct virtnet_info *vi)
>>  {
>> +	cpumask_var_t cpumask;
>>  	int i;
>>  	int cpu;
>>  
>> @@ -1100,15 +1087,21 @@ static void virtnet_set_affinity(struct virtnet_info *vi)
>>  		return;
>>  	}
>>  
>> +	if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
>> +		return;
>> +
>>  	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;
>> +		cpumask_clear(cpumask);
>> +		cpumask_set_cpu(cpu, cpumask);
>> +		netif_set_xps_queue(vi->dev, cpumask, i);
>>  		i++;
>>  	}
>>  
>>  	vi->affinity_hint_set = true;
>> +	free_cpumask_var(cpumask);
>>  }
> Um, isn't this just cpumask_of(cpu)?

True, I thought it should be somewhat more easier.

Will post V2.
>
> Cheers,
> Rusty.
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