Date: Tue, 5 Aug 2003 16:53:02 -0700 (PDT) From: John Polstra <jdp@polstra.com> To: net@freebsd.org Cc: sam@errno.com Subject: Re: bpf, ipfw and before-and-after Message-ID: <200308052353.h75Nr2qC007206@strings.polstra.com> In-Reply-To: <1564916751.1060101774@melange.errno.com> References: <20030805133922.GA7713@k7.mavetju> <01ca01c35b86$83c75590$812a40c1@PETEX31> <200308052101.h75L1WR1006787@strings.polstra.com> <1564916751.1060101774@melange.errno.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. John -- John Polstra John D. Polstra & Co., Inc. Seattle, Washington USA "Two buttocks cannot avoid friction." -- Malawi saying
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