Re: bpf, ipfw and before-and-after

From: Sam Leffler (sam_at_errno.com)
Date: 08/06/03

  • Next message: John Polstra: "Re: bpf, ipfw and before-and-after" 
    Date: Tue, 05 Aug 2003 16:42:55 -0700
To: John Polstra <jdp@polstra.com>, net@freebsd.org

    > In article <01ca01c35b86$83c75590$812a40c1@PETEX31>,
    > Petri Helenius <pete@he.iki.fi> wrote:
    >> >
    >> > This would add additional delays to the code path for both ingress
    >> > and egress. In a world where gigabit ethernet is becoming the norm,
    >> > every nanosecond counts. I don't think the benefits of your proposal
    >> > would justify the performance loss. At the very least, I'd want the
    >> > extra calls to bpf_mtap to be present in the code only if enabled by
    >> > an option in the kernel config file.
    >> >
    >> bpf is slow by design because the design mandates a packet copy.
    >>
    >> Itīs not a justification to make it slower but gigabit performance out
    >> of bpf is just not there until memory speeds increase a lot or the
    >> copying goes away.
    >
    > My point is that the extra calls to bpf_mtap would harm performance
    > even when bpf wasn't being used.

    In -current I believe all the calls are prefixed with a check for
    ifp->if_bpf or similar. So any slow down should only happen when BPF is
    active.

            Sam

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