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Date: Tue, 05 Aug 2003 16:42:55 -0700
From: Sam Leffler <sam@errno.com>
To: John Polstra <jdp@polstra.com>, net@freebsd.org
Message-ID: <1564916751.1060101774@melange.errno.com>
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References: <20030805133922.GA7713@k7.mavetju>
 	<200308051817.h75IH7jb006622@strings.polstra.com>
 	<01ca01c35b86$83c75590$812a40c1@PETEX31>
 <200308052101.h75L1WR1006787@strings.polstra.com>
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Subject: Re: bpf, ipfw and before-and-after
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> 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.
>>
>> It=B4s 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=20
ifp->if_bpf or similar.  So any slow down should only happen when BPF is=20
active.

	Sam