netdev - Re: [RFC PATCH 5/9] virtio_net: build xdp

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Date:   Thu, 8 Dec 2022 16:25:15 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC PATCH 5/9] virtio_net: build xdp_buff with multi buffers



在 2022/12/6 下午2:14, Jason Wang 写道:
> On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>> Support xdp for multi buffer packets.
>>
>> Putting the first buffer as the linear part for xdp_buff,
>> and the rest of the buffers as non-linear fragments to struct
>> skb_shared_info in the tailroom belonging to xdp_buff.
>>
>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>> ---
>>   drivers/net/virtio_net.c | 74 ++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 74 insertions(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index cd65f85d5075..20784b1d8236 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -911,6 +911,80 @@ static struct sk_buff *receive_big(struct net_device *dev,
>>          return NULL;
>>   }
>>
>> +static int virtnet_build_xdp_buff(struct net_device *dev,
>> +                                 struct virtnet_info *vi,
>> +                                 struct receive_queue *rq,
>> +                                 struct xdp_buff *xdp,
>> +                                 void *buf,
>> +                                 unsigned int len,
>> +                                 unsigned int frame_sz,
>> +                                 u16 *num_buf,
>> +                                 unsigned int *xdp_frags_truesize,
>> +                                 struct virtnet_rq_stats *stats)
>> +{
>> +       unsigned int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>> +       struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
>> +       unsigned int truesize, headroom;
>> +       struct skb_shared_info *shinfo;
>> +       unsigned int xdp_frags_truesz = 0;
>> +       unsigned int cur_frag_size;
>> +       struct page *page;
>> +       skb_frag_t *frag;
>> +       int offset;
>> +       void *ctx;
>> +
>> +       xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
>> +       xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
>> +                        VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
>> +       shinfo = xdp_get_shared_info_from_buff(xdp);
>> +       shinfo->nr_frags = 0;
>> +       shinfo->xdp_frags_size = 0;
>> +
>> +       if ((*num_buf - 1) > MAX_SKB_FRAGS)
>> +               return -EINVAL;
>> +
>> +       while ((--*num_buf) >= 1) {
>> +               buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> So this works only for a mergeable buffer, I wonder if it's worth it
> to make it work for big mode as well. Or at least we can mention it as
> a TODO somewhere and rename this function (with mergeable suffix).

Yes, I'm leaning towards the latter, I'll rename it with a mergeable 
suffix in the next version.

Thanks.

>
> Others look good.
>
> Thanks
>
>> +               if (unlikely(!buf)) {
>> +                       pr_debug("%s: rx error: %d buffers out of %d missing\n",
>> +                                dev->name, *num_buf,
>> +                                virtio16_to_cpu(vi->vdev, hdr->num_buffers));
>> +                       dev->stats.rx_length_errors++;
>> +                       return -EINVAL;
>> +               }
>> +
>> +               if (!xdp_buff_has_frags(xdp))
>> +                       xdp_buff_set_frags_flag(xdp);
>> +
>> +               stats->bytes += len;
>> +               page = virt_to_head_page(buf);
>> +               offset = buf - page_address(page);
>> +               truesize = mergeable_ctx_to_truesize(ctx);
>> +               headroom = mergeable_ctx_to_headroom(ctx);
>> +
>> +               cur_frag_size = truesize + (headroom ? (headroom + tailroom) : 0);
>> +               xdp_frags_truesz += cur_frag_size;
>> +               if (unlikely(len > truesize || cur_frag_size > PAGE_SIZE)) {
>> +                       pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
>> +                                dev->name, len, (unsigned long)ctx);
>> +                       dev->stats.rx_length_errors++;
>> +                       return -EINVAL;
>> +               }
>> +
>> +               frag = &shinfo->frags[shinfo->nr_frags++];
>> +               __skb_frag_set_page(frag, page);
>> +               skb_frag_off_set(frag, offset);
>> +               skb_frag_size_set(frag, len);
>> +               if (page_is_pfmemalloc(page))
>> +                       xdp_buff_set_frag_pfmemalloc(xdp);
>> +
>> +               shinfo->xdp_frags_size += len;
>> +       }
>> +
>> +       *xdp_frags_truesize = xdp_frags_truesz;
>> +       return 0;
>> +}
>> +
>>   static struct sk_buff *receive_mergeable(struct net_device *dev,
>>                                           struct virtnet_info *vi,
>>                                           struct receive_queue *rq,
>> --
>> 2.19.1.6.gb485710b
>>