Subject: Re: [PATCH net-next v3] virtio-net: page_to_skb() use build_skb when there's sufficient tailroom

From: David Ahern <[email-masked]>
Date: Mon, 19 Apr 2021 09:48:16 -0700

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.