linux-kernel - Re: [net-next RFC V5 4/5] virtio

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Date:	Fri, 06 Jul 2012 04:02:58 +0800
From:	Amos Kong <akong@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
CC:	mst@...hat.com, mashirle@...ibm.com, krkumar2@...ibm.com,
	habanero@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, edumazet@...gle.com,
	tahm@...ux.vnet.ibm.com, jwhan@...ewood.snu.ac.kr,
	davem@...emloft.net, kvm@...r.kernel.org, sri@...ibm.com
Subject: Re: [net-next RFC V5 4/5] virtio_net: multiqueue support

On 07/05/2012 06:29 PM, Jason Wang wrote:
> This patch converts virtio_net to a multi queue device. After negotiated
> VIRTIO_NET_F_MULTIQUEUE feature, the virtio device has many tx/rx queue pairs,
> and driver could read the number from config space.
> 
> The driver expects the number of rx/tx queue paris is equal to the number of
> vcpus. To maximize the performance under this per-cpu rx/tx queue pairs, some
> optimization were introduced:
> 
> - Txq selection is based on the processor id in order to avoid contending a lock
>   whose owner may exits to host.
> - Since the txq/txq were per-cpu, affinity hint were set to the cpu that owns
>   the queue pairs.
> 
> Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---

...

>  
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
> -	int err;
> +	int i, err;
>  	struct net_device *dev;
>  	struct virtnet_info *vi;
> +	u16 num_queues, num_queue_pairs;
> +
> +	/* Find if host supports multiqueue virtio_net device */
> +	err = virtio_config_val(vdev, VIRTIO_NET_F_MULTIQUEUE,
> +				offsetof(struct virtio_net_config,
> +				num_queues), &num_queues);
> +
> +	/* We need atleast 2 queue's */


s/atleast/at least/


> +	if (err || num_queues < 2)
> +		num_queues = 2;
> +	if (num_queues > MAX_QUEUES * 2)
> +		num_queues = MAX_QUEUES;

                num_queues = MAX_QUEUES * 2;

MAX_QUEUES is the limitation of RX or TX.

> +
> +	num_queue_pairs = num_queues / 2;

...

-- 
			Amos.
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