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

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Message-Id: <20150607.020153.2078872410885973154.davem@davemloft.net>
Date:	Sun, 07 Jun 2015 02:01:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	edumazet@...gle.com, jhs@...atatu.com, daniel@...earbox.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 1/2] bpf: make programs see skb->data == L2
 for ingress and egress

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Thu,  4 Jun 2015 10:11:53 -0700

> 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 <ast@...mgrid.com>

Applied.
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