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Date: Wed, 14 Jul 2010 22:52:40 -0400 From: Bill Fink <billfink@...dspring.com> To: David Miller <davem@...emloft.net> Cc: davidsen@....com, lists@...dgooses.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: Raise initial congestion window size / speedup slow start? On Wed, 14 Jul 2010, David Miller wrote: > From: Bill Davidsen <davidsen@....com> > Date: Wed, 14 Jul 2010 11:21:15 -0400 > > > You may have to go into /proc/sys/net/core and crank up the > > rmem_* settings, depending on your distribution. > > You should never, ever, have to touch the various networking sysctl > values to get good performance in any normal setup. If you do, it's a > bug, report it so we can fix it. > > I cringe every time someone says to do this, so please do me a favor > and don't spread this further. :-) > > For one thing, TCP dynamically adjusts the socket buffer sizes based > upon the behavior of traffic on the connection. > > And the TCP memory limit sysctls (not the core socket ones) are sized > based upon available memory. They are there to protect you from > situations such as having so much memory dedicated to socket buffers > that there is none left to do other things effectively. It's a > protective limit, rather than a setting meant to increase or improve > performance. So like the others, leave these alone too. What's normal? :-) netem1% cat /proc/version Linux version 2.6.30.10-105.2.23.fc11.x86_64 (mockbuild@...-01.phx2.fedoraproject.org) (gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) (GCC) ) #1 SMP Thu Feb 11 07:06:34 UTC 2010 Linux TCP autotuning across an 80 ms RTT cross country network path: netem1% nuttcp -T10 -i1 192.168.1.18 14.1875 MB / 1.00 sec = 119.0115 Mbps 0 retrans 558.0000 MB / 1.00 sec = 4680.7169 Mbps 0 retrans 872.8750 MB / 1.00 sec = 7322.3527 Mbps 0 retrans 869.6875 MB / 1.00 sec = 7295.5478 Mbps 0 retrans 858.4375 MB / 1.00 sec = 7201.0165 Mbps 0 retrans 857.3750 MB / 1.00 sec = 7192.2116 Mbps 0 retrans 865.5625 MB / 1.00 sec = 7260.7193 Mbps 0 retrans 872.3750 MB / 1.00 sec = 7318.2095 Mbps 0 retrans 862.7500 MB / 1.00 sec = 7237.2571 Mbps 0 retrans 857.6250 MB / 1.00 sec = 7194.1864 Mbps 0 retrans 7504.2771 MB / 10.09 sec = 6236.5068 Mbps 11 %TX 25 %RX 0 retrans 80.59 msRTT Manually specified 100 MB TCP socket buffer on the same path: netem1% nuttcp -T10 -i1 -w100m 192.168.1.18 106.8125 MB / 1.00 sec = 895.9598 Mbps 0 retrans 1092.0625 MB / 1.00 sec = 9160.3254 Mbps 0 retrans 1111.2500 MB / 1.00 sec = 9322.6424 Mbps 0 retrans 1115.4375 MB / 1.00 sec = 9356.2569 Mbps 0 retrans 1116.4375 MB / 1.00 sec = 9365.6937 Mbps 0 retrans 1115.3125 MB / 1.00 sec = 9356.2749 Mbps 0 retrans 1121.2500 MB / 1.00 sec = 9405.6233 Mbps 0 retrans 1125.5625 MB / 1.00 sec = 9441.6949 Mbps 0 retrans 1130.0000 MB / 1.00 sec = 9478.7479 Mbps 0 retrans 1139.0625 MB / 1.00 sec = 9555.8559 Mbps 0 retrans 10258.5120 MB / 10.20 sec = 8440.3558 Mbps 15 %TX 40 %RX 0 retrans 80.59 msRTT The manually selected TCP socket buffer size both ramps up quicker and achieves a much higher steady state rate. -Bill -- 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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