bpf, ipfw and before-and-after
sam at errno.com
Tue Aug 5 17:05:47 PDT 2003
> In article <1564916751.1060101774 at melange.errno.com>,
> Sam Leffler <sam at errno.com> wrote:
>> > 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
> That does not follow, because the check of ifp->if_bpf itself takes
> time. There is no way to avoid the performance penalty except at
> compile time. Yes, branch prediction helps, but it doesn't eliminate
> the problem. Even with gigabit ethernet those individual nanoseconds
> add up quickly to the point where they matter. With 10 Gb ethernet on
> the way, it will only get worse.
You said there were calls to bpf_mtag and they would add noticeable
overhead even when BPF was not in use. I said these are only made when BPF
is in use. What doesn't follow?
I'm not arguing about keeping up with 10Gb media...
More information about the freebsd-net