Date: Mon, 7 Jul 2008 15:15:50 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: Bruce Evans <brde@optusnet.com.au> Cc: FreeBSD Net <freebsd-net@FreeBSD.org>, Andre Oppermann <andre@FreeBSD.org>, Ingo Flaschberger <if@xip.at>, Paul <paul@gtcomm.net> Subject: Re: Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp] Message-ID: <20080707131550.GA69202@owl.midgard.homeip.net> In-Reply-To: <20080707213356.G7572@besplex.bde.org> References: <486D35A0.4000302@gtcomm.net> <alpine.LFD.1.10.0807041106591.19613@filebunker.xip.at> <486DF1A3.9000409@gtcomm.net> <alpine.LFD.1.10.0807041303490.20760@filebunker.xip.at> <486E65E6.3060301@gtcomm.net> <alpine.LFD.1.10.0807052356130.2145@filebunker.xip.at> <4871DB8E.5070903@freebsd.org> <20080707191918.B4703@besplex.bde.org> <4871FB66.1060406@freebsd.org> <20080707213356.G7572@besplex.bde.org>
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On Mon, Jul 07, 2008 at 10:30:53PM +1000, Bruce Evans wrote: > On Mon, 7 Jul 2008, Andre Oppermann wrote: > > > Bruce Evans wrote: > >> What are the other overheads? I calculate 1.644Mpps counting the > >> inter-frame > >> gap, with 64-byte packets and 64-header_size payloads. If the 64 bytes > >> is for the payload, then the max is much lower. > > > > The theoretical maximum at 64byte frames is 1,488,100. I've looked > > up my notes the 1.244Mpps number can be ajusted to 1.488Mpps. > > Where is the extra? I still get 1.644736 Mpps (10^9/(8*64+96)). > 1.488095 is for 64 bits extra (10^9/(8*64+96+64)). A standard ethernet frame (on the wire) consists of: 7 octets preamble 1 octet Start Frame Delimiter 6 octets destination address 6 octets source address 2 octets length/type 46-1500 octets data (+padding if needed) 4 octets Frame Check Sequence Followed by (at least) 96 bits interFrameGap, before the next frame starts. For minimal packet size this gives a maximum packet rate at 1Gbit/s of 1e9/((7+1+6+6+2+46+4)*8+96)/ = 1488095 packets/second You probably missed the preamble and start frame delimiter in your calculation. -- <Insert your favourite quote here.> Erik Trulsson ertr1013@student.uu.se
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