netdev - Re: [PATCH net-next 2/8] virtio_net: mergeable xdp: introduce mergeable_xdp

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Date:   Thu, 23 Mar 2023 19:04:20 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        <virtualization@...ts.linux-foundation.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH net-next 2/8] virtio_net: mergeable xdp: introduce mergeable_xdp_prepare

On Thu, 23 Mar 2023 15:24:38 +0800, Yunsheng Lin <linyunsheng@...wei.com> wrote:
> On 2023/3/23 13:40, Jason Wang wrote:
> >>>
> >>>>
> >>>> Also, it seems better to split the xdp_linearize_page() to two functions
> >>>> as pskb_expand_head() and __skb_linearize() do, one to expand the headroom,
> >>>> the other one to do the linearizing.
> >>>
> >>> No skb here.
> >>
> >> I means following the semantics of pskb_expand_head() and __skb_linearize(),
> >> not to combine the headroom expanding and linearizing into one function as
> >> xdp_linearize_page() does now if we want a better refoctor result.
> >
> > Not sure it's worth it, since the use is very specific unless we could
> > find a case that wants only one of them.
>
> It seems receive_small() only need the headroom expanding one.
> For receive_mergeable(), it seems we can split into the below cases:
> 1. " (!xdp_prog->aux->xdp_has_frags && (num_buf > 1 || headroom < virtnet_get_headroom(vi)))"
>    case only need linearizing.
> 2. other cases only need headroom/tailroom expanding.
>
> Anyway, it is your call to decide if you want to take this
> opportunity do a better refoctoring to virtio_net.

Compared to the chaotic state of the virtio-net XDP, this is a small point.
And I don’t think this brings any practical optimization. If you think this
division is better. You can submit a new patch on the top of this patch set.
I think the code can be clearer.

Thanks.

>
> >
> > Thanks
> >
> >>
> >>>
> >>>
> >>>>
> >>
> >
> >
> > .
> >