Messages in this thread | | | Subject | Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling | From | Jason Wang <> | Date | Thu, 30 Mar 2017 11:53:15 +0800 |
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On 2017年03月30日 10:33, Michael S. Tsirkin wrote: > On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote: >> >> 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@redhat.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 > Same comment about a compiler barrier applies then.
Ok, rethink about this, since skb_array could be resized, using lockless version seems wrong.
For the comment of using compiler barrier, caller (vhost_net_rx_peek_head_len) uses cpu_relax(). But I haven't figured out why a compiler barrier is needed here. Could you please explain?
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
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