Re: [RFC PATCH net-next 10/12] vhost_net: build xdp buff

Jason Wang
2018-05-22T12:41:20Z

On 2018年05月22日 00:56, Jesse Brandeburg wrote:
> On Mon, 21 May 2018 17:04:31 +0800 Jason wrote:
>> This patch implement build XDP buffers in vhost_net. The idea is do
>> userspace copy in vhost_net and build XDP buff based on the
>> page. Vhost_net can then submit one or an array of XDP buffs to
>> underlayer socket (e.g TUN). TUN can choose to do XDP or call
>> build_skb() to build skb. To support build skb, vnet header were also
>> stored into the header of the XDP buff.
>>
>> This userspace copy and XDP buffs building is key to achieve XDP
>> batching in TUN, since TUN does not need to care about userspace copy
>> and then can disable premmption for several XDP buffs to achieve
>> batching from XDP.
>>
>> TODO: reserve headroom based on the TUN XDP.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> drivers/vhost/net.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 74 insertions(+)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index f0639d7..1209e84 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -492,6 +492,80 @@ static bool vhost_has_more_pkts(struct vhost_net *net,
>> likely(!vhost_exceeds_maxpend(net));
>> }
>>
>> +#define VHOST_NET_HEADROOM 256
>> +#define VHOST_NET_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)
>> +
>> +static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>> + struct iov_iter *from,
>> + struct xdp_buff *xdp)
>> +{
>> + struct vhost_virtqueue *vq = &nvq->vq;
>> + struct page_frag *alloc_frag = &current->task_frag;
>> + struct virtio_net_hdr *gso;
>> + size_t len = iov_iter_count(from);
>> + int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>> + int pad = SKB_DATA_ALIGN(VHOST_NET_RX_PAD + VHOST_NET_HEADROOM
>> + + nvq->sock_hlen);
>> + int sock_hlen = nvq->sock_hlen;
>> + void *buf;
>> + int copied;
>> +
>> + if (len < nvq->sock_hlen)
>> + return -EFAULT;
>> +
>> + if (SKB_DATA_ALIGN(len + pad) +
>> + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
>> + return -ENOSPC;
>> +
>> + buflen += SKB_DATA_ALIGN(len + pad);
> maybe store the result of SKB_DATA_ALIGN in a local instead of doing
> the work twice?

Ok.

>
>> + alloc_frag->offset = ALIGN((u64)alloc_frag->offset, SMP_CACHE_BYTES);
>> + if (unlikely(!skb_page_frag_refill(buflen, alloc_frag, GFP_KERNEL)))
>> + return -ENOMEM;
>> +
>> + buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
>> +
>> + /* We store two kinds of metadata in the header which will be
>> + * used for XDP_PASS to do build_skb():
>> + * offset 0: buflen
>> + * offset sizeof(int): vnet header
>> + */
>> + copied = copy_page_from_iter(alloc_frag->page,
>> + alloc_frag->offset + sizeof(int), sock_hlen, from);
>> + if (copied != sock_hlen)
>> + return -EFAULT;
>> +
>> + gso = (struct virtio_net_hdr *)(buf + sizeof(int));
>> +
>> + if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
>> + vhost16_to_cpu(vq, gso->csum_start) +
>> + vhost16_to_cpu(vq, gso->csum_offset) + 2 >
>> + vhost16_to_cpu(vq, gso->hdr_len)) {
>> + gso->hdr_len = cpu_to_vhost16(vq,
>> + vhost16_to_cpu(vq, gso->csum_start) +
>> + vhost16_to_cpu(vq, gso->csum_offset) + 2);
>> +
>> + if (vhost16_to_cpu(vq, gso->hdr_len) > len)
>> + return -EINVAL;
>> + }
>> +
>> + len -= sock_hlen;
>> + copied = copy_page_from_iter(alloc_frag->page,
>> + alloc_frag->offset + pad,
>> + len, from);
>> + if (copied != len)
>> + return -EFAULT;
>> +
>> + xdp->data_hard_start = buf;
>> + xdp->data = buf + pad;
>> + xdp->data_end = xdp->data + len;
>> + *(int *)(xdp->data_hard_start)= buflen;
> space before =

Yes.

Thanks

>
>> +
>> + get_page(alloc_frag->page);
>> + alloc_frag->offset += buflen;
>> +
>> + return 0;
>> +}
>> +
>> static void handle_tx_copy(struct vhost_net *net)
>> {
>> struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];