netdev - Re: [PATCH net-next v3] virtio-net: page_to_skb() use build

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Date:   Tue, 20 Apr 2021 10:49:18 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     David Ahern <dsahern@...il.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v3] virtio-net: page_to_skb() use build_skb when
 there's sufficient tailroom


在 2021/4/20 上午12:48, David Ahern 写道:
> On 4/16/21 2:16 AM, Xuan Zhuo wrote:
>> In page_to_skb(), if we have enough tailroom to save skb_shared_info, we
>> can use build_skb to create skb directly. No need to alloc for
>> additional space. And it can save a 'frags slot', which is very friendly
>> to GRO.
>>
>> Here, if the payload of the received package is too small (less than
>> GOOD_COPY_LEN), we still choose to copy it directly to the space got by
>> napi_alloc_skb. So we can reuse these pages.
>>
>> Testing Machine:
>>      The four queues of the network card are bound to the cpu1.
>>
>> Test command:
>>      for ((i=0;i<5;++i)); do sockperf tp --ip 192.168.122.64 -m 1000 -t 150& done
>>
>> The size of the udp package is 1000, so in the case of this patch, there
>> will always be enough tailroom to use build_skb. The sent udp packet
>> will be discarded because there is no port to receive it. The irqsoftd
>> of the machine is 100%, we observe the received quantity displayed by
>> sar -n DEV 1:
>>
>> no build_skb:  956864.00 rxpck/s
>> build_skb:    1158465.00 rxpck/s
>>
> virtio_net is using napi_consume_skb, so napi_build_skb should show a
> small increase from build_skb.
>

Yes and we probably need to do this in receive_small().

Thanks