Date: Tue, 05 Aug 2003 17:05:42 -0700 From: Sam Leffler <sam@errno.com> To: John Polstra <jdp@polstra.com>, net@freebsd.org Subject: Re: bpf, ipfw and before-and-after Message-ID: <1566283957.1060103142@melange.errno.com> In-Reply-To: <200308052353.h75Nr2qC007206@strings.polstra.com> References: <20030805133922.GA7713@k7.mavetju> <01ca01c35b86$83c75590$812a40c1@PETEX31> <200308052101.h75L1WR1006787@strings.polstra.com> <1564916751.1060101774@melange.errno.com> <200308052353.h75Nr2qC007206@strings.polstra.com>
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> In article <1564916751.1060101774@melange.errno.com>, > Sam Leffler <sam@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 >> active. > > 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... Sam
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