Subject: Re: [PATCH v2 net-next 1/2] bpf: make programs see skb->data == L2 for ingress and egress

From: Jamal Hadi Salim <[email-masked]>
Date: Fri, 05 Jun 2015 06:03:15 -0400

On 06/04/15 13:11, Alexei Starovoitov wrote:
> eBPF programs attached to ingress and egress qdiscs see inconsistent skb->data.
> For ingress L2 header is already pulled, whereas for egress it's present.
> This is known to program writers which are currently forced to use
> BPF_LL_OFF workaround.
> Since programs don't change skb internal pointers it is safe to do
> pull/push right around invocation of the program and earlier taps and
> later pt->func() will not be affected.
> Multiple taps via packet_rcv(), tpacket_rcv() are doing the same trick
> around run_filter/BPF_PROG_RUN even if skb_shared.
>
> This fix finally allows programs to use optimized LD_ABS/IND instructions
> without BPF_LL_OFF for higher performance.
> tc ingress + cls_bpf + samples/bpf/tcbpf1_kern.o
>         w/o JIT   w/JIT
> before  20.5     23.6 Mpps
> after   21.8     26.6 Mpps
>
> Old programs with BPF_LL_OFF will still work as-is.
>
> We can now undo most of the earlier workaround commit:
> a166151cbe33 ("bpf: fix bpf helpers to use skb->mac_header relative offsets")
>
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> ---

Acked-by: Jamal Hadi Salim <[email-masked]>

cheers,
jamal