netdev - Re: [PATCH v2 0/9] virtio_net: support multi buffer xdp

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Date:   Mon, 26 Dec 2022 10:32:53 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "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>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v2 0/9] virtio_net: support multi buffer xdp


Hi Jason, do you have any comments on this?

Thanks.

在 2022/12/20 下午10:14, Heng Qi 写道:
> Changes since RFC:
> - Using headroom instead of vi->xdp_enabled to avoid re-reading
>    in add_recvbuf_mergeable();
> - Disable GRO_HW and keep linearization for single buffer xdp;
> - Renamed to virtnet_build_xdp_buff_mrg();
> - pr_debug() to netdev_dbg();
> - Adjusted the order of the patch series.
>
> Currently, virtio net only supports xdp for single-buffer packets
> or linearized multi-buffer packets. This patchset supports xdp for
> multi-buffer packets, then larger MTU can be used if xdp sets the
> xdp.frags. This does not affect single buffer handling.
>
> In order to build multi-buffer xdp neatly, we integrated the code
> into virtnet_build_xdp_buff_mrg() for xdp. The first buffer is used
> for prepared xdp buff, and the rest of the buffers are added to
> its skb_shared_info structure. This structure can also be
> conveniently converted during XDP_PASS to get the corresponding skb.
>
> Since virtio net uses comp pages, and bpf_xdp_frags_increase_tail()
> is based on the assumption of the page pool,
> (rxq->frag_size - skb_frag_size(frag) - skb_frag_off(frag))
> is negative in most cases. So we didn't set xdp_rxq->frag_size in
> virtnet_open() to disable the tail increase.
>
> Heng Qi (9):
>    virtio_net: disable the hole mechanism for xdp
>    virtio_net: set up xdp for multi buffer packets
>    virtio_net: update bytes calculation for xdp_frame
>    virtio_net: build xdp_buff with multi buffers
>    virtio_net: construct multi-buffer xdp in mergeable
>    virtio_net: transmit the multi-buffer xdp
>    virtio_net: build skb from multi-buffer xdp
>    virtio_net: remove xdp related info from page_to_skb()
>    virtio_net: support multi-buffer xdp
>
>   drivers/net/virtio_net.c | 332 ++++++++++++++++++++++++++-------------
>   1 file changed, 219 insertions(+), 113 deletions(-)
>