On 07/16, Jason Xing wrote:
> From: Jason Xing <kernelxing@xxxxxxxxxxx>
>
> This patch only does one thing that removes validate_xmit_skb_list()
> for xsk.
>
> For xsk, it's not needed to validate and check the skb in
> validate_xmit_skb_list() in copy mode because xsk_build_skb() doesn't
> and doesn't need to prepare those requisites to validate. Xsk is just
> responsible for delivering raw data from userspace to the driver.
>
> The __dev_direct_xmit was taken out of af_packet in commit 865b03f21162
> ("dev: packet: make packet_direct_xmit a common function"). And a call
> to validate_xmit_skb_list was added in commit 104ba78c9880 ("packet: on
> direct_xmit, limit tso and csum to supported devices") to support TSO.
> Since we don't support tso/vlan offloads in xsk_build_skb, we can remove
> validate_xmit_skb_list for xsk. Skipping numerous checks somehow
> contributes to the transmission especially in the extremely hot path.
>
> Performance-wise, I used './xdpsock -i enp2s0f0np0 -t -S -s 64' to verify
> the guess and then measured on the machine with ixgbe driver. It stably
> goes up by 5.48%, which can be seen in the shown below:
> Before:
> sock0@enp2s0f0np0:0 txonly xdp-skb
> pps pkts 1.00
> rx 0 0
> tx 1,187,410 3,513,536
> After:
> sock0@enp2s0f0np0:0 txonly xdp-skb
> pps pkts 1.00
> rx 0 0
> tx 1,252,590 2,459,456
>
> This patch also removes total ~4% consumption which can be observed
> by perf:
> |--2.97%--validate_xmit_skb
> | |
> | --1.76%--netif_skb_features
> | |
> | --0.65%--skb_network_protocol
> |
> |--1.06%--validate_xmit_xfrm
>
> Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> ---
> V2
> Link: https://lore.kernel.org/all/20250713025756.24601-1-kerneljasonxing@xxxxxxxxx/
> 1. avoid adding a new flag
> 2. add more descriptions from Stan
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
LGTM, but would be nice if Willem or Magnus can chime in to confirm that
it's safe.
