On Fri, 2017-04-14 at 12:41 -0700, Alexei Starovoitov wrote: > > ahh. i thought all drivers do at least copy-break (256) bytes We do copy-break, but that's only applicable when there's no non-linear data left afterwards :) > or copy > get_headlen or build_skb the whole thing. > Since wireless does eth_hlen, then yeah, skb_linearize() is the only > way. It's rather difficult to do this in wifi because we'd need to parse deep into the packet - at a point where we haven't even parsed the 802.11 header (which has variable length) fully. So that leaves us to do it at the very end, after conversion to ethernet format, but then it feels pointless since we might as well let the rest of the stack do it. > I guess any driver that would care about XDP performance would either > implement in-driver XDP or make sure that skb_linearize() doesn't > happen in generic XDP by doing build_skb() with the whole packet. > The driver can be smart and avoid doing copy-break if generic XDP is > on. Indeed. I think this is less about performance than ease of experimentation. johannes
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