Subject: Re: [PATCH V2 2/2] virtio-net: reset virtqueue affinity when doing cpu hotplug

From: Jason Wang <[email-masked]>
Date: Mon, 07 Jan 2013 15:28:47 +0800

On 01/07/2013 03:15 PM, Wanlong Gao wrote:
> Add a cpu notifier to virtio-net, so that we can reset the
> virtqueue affinity if the cpu hotplug happens. It improve
> the performance through enabling or disabling the virtqueue
> affinity after doing cpu hotplug.
> Adding the notifier block to virtnet_info is suggested by
> Jason, thank you.
>
> Cc: Rusty Russell <[email-masked]>
> Cc: "Michael S. Tsirkin" <[email-masked]>
> Cc: Jason Wang <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Wanlong Gao <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b483fb5..9547b4c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -26,6 +26,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/if_vlan.h>
>  #include <linux/slab.h>
> +#include <linux/cpu.h>
>  
>  static int napi_weight = 128;
>  module_param(napi_weight, int, 0444);
> @@ -123,6 +124,9 @@ struct virtnet_info {
>  
>  	/* Does the affinity hint is set for virtqueues? */
>  	bool affinity_hint_set;
> +
> +	/* CPU hot plug notifier */
> +	struct notifier_block nb;
>  };
>  
>  struct skb_vnet_hdr {
> @@ -1051,6 +1055,23 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
>  	}
>  }
>  
> +static int virtnet_cpu_callback(struct notifier_block *nfb,
> +			        unsigned long action, void *hcpu)
> +{
> +	struct virtnet_info *vi = container_of(nfb, struct virtnet_info, nb);
> +	switch(action) {
> +	case CPU_ONLINE:
> +	case CPU_ONLINE_FROZEN:
> +	case CPU_DEAD:
> +	case CPU_DEAD_FROZEN:
> +		virtnet_set_affinity(vi, true);
> +		break;
> +	default:
> +		break;
> +	}
> +	return NOTIFY_OK;
> +}
> +

I think you'd better fix the .ndo_select_queue() as well (as Michael
said in your V1) since it currently uses smp processor id which may not
work very well in this case also.

Thanks
>  static void virtnet_get_ringparam(struct net_device *dev,
>  				struct ethtool_ringparam *ring)
>  {
> @@ -1509,6 +1530,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		}
>  	}
>  
> +	vi->nb.notifier_call = &virtnet_cpu_callback;
> +	err = register_hotcpu_notifier(&vi->nb);
> +	if (err) {
> +		pr_debug("virtio_net: registering cpu notifier failed\n");
> +		goto free_recv_bufs;
> +	}
> +
>  	/* Assume link up if device can't report link status,
>  	   otherwise get link status from config. */
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> @@ -1553,6 +1581,8 @@ static void virtnet_remove(struct virtio_device *vdev)
>  {
>  	struct virtnet_info *vi = vdev->priv;
>  
> +	unregister_hotcpu_notifier(&vi->nb);
> +
>  	/* Prevent config work handler from accessing the device. */
>  	mutex_lock(&vi->config_lock);
>  	vi->config_enable = false;