On 8/4/25 6:18 AM, Jesper Dangaard Brouer wrote:
Do keep-in-mind that "moving skb allocation out of the driver" is not part of this patchset and a moonshot goal that will take a long time (but we are already "simulation" this via XDP-redirect for years now).
The XDP_PASS was first done in the very early days of BPF in 2016. The XDP-redirect then followed a similar setup. A lot has improved since then. A moonshot in 2016 does not necessarily mean it is still hard to do now. e.g. Loop is feasible. Directly reading/writing skb is also easier.
Let’s first quantify what the performance loss would be if the skb is allocated and field-set by the xdp prog (for the general XDP_PASS case and the redirect+cpumap case). If it’s really worth it, let’s see what it would take for the XDP program to achieve similar optimizations.
Drivers should obviously not unconditionally populate the xdp_frame's rx_meta area. It is first time to populate rx_meta, once driver reach
afaict, the rx_meta is reserved regardless though. The xdp prog cannot use that space for data_meta. The rx_meta will grow in time.
My preference is to allow xdp prog to decide what needs to write in data_meta and decides what needs to set in the skb directly. This is the general case it should support first and then optimize.
