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

[Jason Wang]

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