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

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Message-ID: <00509559-f3b6-2914-76f4-39e9e96f37c1@huawei.com>
Date:   Thu, 23 Mar 2023 15:24:38 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "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>
Subject: Re: [PATCH net-next 2/8] virtio_net: mergeable xdp: introduce
 mergeable_xdp_prepare

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.

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