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Date: Wed, 30 Jan 2008 08:01:46 -0600 (CST) From: Bruce Allen <ballen@...vity.phys.uwm.edu> To: netdev@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, David Miller <davem@...emloft.net> cc: Henning Fehrmann <henning.fehrmann@....mpg.de>, Carsten Aulbert <carsten.aulbert@....mpg.de>, Bruce Allen <bruce.allen@....mpg.de> Subject: Re: e1000 full-duplex TCP performance well below wire speed Hi David, Thanks for your note. >> (The performance of a full duplex stream should be close to 1Gb/s in >> both directions.) > > This is not a reasonable expectation. > > ACKs take up space on the link in the opposite direction of the > transfer. > > So the link usage in the opposite direction of the transfer is > very far from zero. Indeed, we are not asking to see 1000 Mb/s. We'd be happy to see 900 Mb/s. Netperf is trasmitting a large buffer in MTU-sized packets (min 1500 bytes). Since the acks are only about 60 bytes in size, they should be around 4% of the total traffic. Hence we would not expect to see more than 960 Mb/s. We have run these same tests on older kernels (with Broadcomm NICS) and gotten above 900 Mb/s full duplex. Cheers, Bruce -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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