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

From: Wanlong Gao <[email-masked]>
Date: Mon, 07 Jan 2013 15:48:16 +0800

On 01/07/2013 03:28 PM, Jason Wang wrote:
> 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.

The bug is we can't get the right txq if the CPU IDs are not consecutive,
right? Do you have any good idea about fixing this? 

Thanks,
Wanlong Gao

> 
> 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;
> 
>