linux-kernel - Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

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Date:   Thu, 30 Mar 2017 10:16:15 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb
 array during busy polling



On 2017年03月29日 20:07, Michael S. Tsirkin wrote:
> On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
>> For the socket that exports its skb array, we can use lockless polling
>> to avoid touching spinlock during busy polling.
>>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/vhost/net.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 53f09f2..41153a3 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
>>   	return len;
>>   }
>>   
>> -static int sk_has_rx_data(struct sock *sk)
>> +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
>>   {
>>   	struct socket *sock = sk->sk_socket;
>>   
>> +	if (rvq->rx_array)
>> +		return !__skb_array_empty(rvq->rx_array);
>> +
>>   	if (sock->ops->peek_len)
>>   		return sock->ops->peek_len(sock);
>>   
> I don't see which patch adds __skb_array_empty.

This is not something new, it was introduced by ad69f35d1dc0a 
("skb_array: array based FIFO for skbs").

Thanks

>
>> @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
>>   		endtime = busy_clock() + vq->busyloop_timeout;
>>   
>>   		while (vhost_can_busy_poll(&net->dev, endtime) &&
>> -		       !sk_has_rx_data(sk) &&
>> +		       !sk_has_rx_data(rvq, sk) &&
>>   		       vhost_vq_avail_empty(&net->dev, vq))
>>   			cpu_relax();
>>   
>> -- 
>> 2.7.4