Date: Mon, 7 Jul 2008 22:30:53 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Andre Oppermann <andre@FreeBSD.org> Cc: FreeBSD Net <freebsd-net@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: <20080707213356.G7572@besplex.bde.org> In-Reply-To: <4871FB66.1060406@freebsd.org> References: <4867420D.7090406@gtcomm.net> <20080701033117.GH83626@cdnetworks.co.kr> <ea7b9c170806302050p2a3a5480t29923a4ac2d7c852@mail.gmail.com> <4869ACFC.5020205@gtcomm.net> <4869B025.9080006@gtcomm.net> <486A7E45.3030902@gtcomm.net> <486A8F24.5010000@gtcomm.net> <486A9A0E.6060308@elischer.org> <486B41D5.3060609@gtcomm.net> <alpine.LFD.1.10.0807021052041.557@filebunker.xip.at> <486B4F11.6040906@gtcomm.net> <alpine.LFD.1.10.0807021155280.557@filebunker.xip.at> <486BC7F5.5070604@gtcomm.net> <20080703160540.W6369@delplex.bde.org> <486C7F93.7010308@gtcomm.net> <20080703195521.O6973@delplex.bde.org> <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>
next in thread | previous in thread | raw e-mail | index | archive | help
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)). >>>> I hoped to reach 1Mpps with the hardware I mentioned some mails before, >>>> but 2Mpps is far far away. >>>> Currently I get 160kpps via pci-32mbit-33mhz-1,2ghz mobile pentium. >>> >>> This is more or less expected. PCI32 is not able to sustain high >>> packet rates. The bus setup times kill the speed. For larger packets >>> the ratio gets much better and some reasonable throughput can be achieved. >> >> I get about 640 kpps without forwarding (sendto: slightly faster; >> recvfrom: slightly slower) on a 2.2GHz A64. Underclocking the memory >> from 200MHz to 100MHz only reduces the speed by about 10%, while not >> overclocking the CPU by 10% reduces the speed by the same 10%, so the >> system is apparently still mainly CPU-bound. > > On PCI32@33MHz? He's using a 1.2GHz Mobile Pentium on top of that. Yes. My example shows that FreeBSD is more CPU-bound than I/O bound up to CPUs considerably faster than a 1.2GHz Pentium (though PentiumM is fast relative to its clock speed). The memory interface may matter more than the CPU clock. >>> NetFPGA doesn't have enough TCAM space to be useful for real routing >>> (as in Internet sized routing table). The trick many embedded networking >>> CPUs use is cache prefetching that is integrated with the network >>> controller. The first 64-128bytes of every packet are transferred >>> automatically into the L2 cache by the hardware. This allows relatively >>> slow CPUs (700 MHz Broadcom BCM1250 in Cisco NPE-G1 or 1.67-GHz Freescale >>> 7448 in NPE-G2) to get more than 1Mpps. Until something like this is >>> possible on Intel or AMD x86 CPUs we have a ceiling limited by RAM speed. >> >> Does using fa$ter memory (speed and/or latency) help here? 64 bytes >> is so small that latency may be more of a problem, especially without >> a prefetch. > > Latency. For IPv4 packet forwarding only one cache line per packet > is fetched. More memory speed only helps with the DMA from/to the > network card. I use low-end memory, but on the machine that does 640 kpps it somehow has latency almost 4 times as low as on new FreeBSD cluster machines (~42 nsec instead of ~150). perfmon (fixed for AXP and A64) and hwpmc report an average of 11 k8-dc-misses per sendto() while sending via bge at 640 kpps. 11 * 42 accounts for 442 nsec out of the 1562 per packet at this rate. 11 * 150 = 1650 would probably make this rate unachievable despite the system having 20 times as much CPU and bus. Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20080707213356.G7572>