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Message-ID: <20081230195858.GA23530@flint.arm.linux.org.uk> Date: Tue, 30 Dec 2008 19:58:58 +0000 From: Russell King <rmk@....linux.org.uk> To: netdev@...r.kernel.org Cc: Ben Hutchings <bhutchings@...arflare.com> Subject: 2.6.27.8 (+the idr fix) TCP Ack issue While trying to access a website on a FC5 machine, I encountered what seemed to be excessive traffic without much progress. tcpdumping the connection showed a permanent stream of acks from both ends of the connection. Ben Hutchings suggested that 607bfbf might fix it, so I built 2.6.27.8 which has this fix in some 20 days ago. After encountering other problems, a fix to lib/idr.c was applied. This kernel seemed to be fine, until... 19:47:32.062670 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: S 3543174870:3543174870(0) win 5840 <mss 1460,sackOK,timestamp 26999689 0,nop,wscale 6> 19:47:32.135812 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: S 3016012818:3016012818(0) ack 3543174871 win 8192 <mss 1276> 19:47:32.135837 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 1 win 5840 19:47:32.135899 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: P 1:644(643) ack 1 win 5840 19:47:32.167644 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 644 win 7073 19:47:32.174366 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: P 1:1190(1189) ack 644 win 7073 19:47:32.174414 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 1190 win 8323 19:47:32.174701 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . 644:3196(2552) ack 1190 win 8323 19:47:32.174720 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: P 3196:3216(20) ack 1190 win 8323 19:47:32.218718 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: P 1190:2215(1025) ack 1920 win 8932 19:47:32.258402 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.285388 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.285397 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.320287 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.320300 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.353016 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.353022 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.382702 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.382712 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.404786 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.404793 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.446827 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.446835 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.451343 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . 1920:3196(1276) ack 2215 win 10701 19:47:32.480976 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.480984 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.530343 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.530356 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.554244 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.554251 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.582139 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.582146 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.613093 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.613121 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 and then it ploughs into ack-madness at as high a speed as the link can handle: 19:47:32.634725 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.634753 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.654389 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.654408 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.674332 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.674339 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.692550 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.692555 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 19:47:32.712249 IP 193.108.74.209.http > dyn-67.arm.linux.org.uk.38803: . ack 3216 win 10701 19:47:32.712265 IP dyn-67.arm.linux.org.uk.38803 > 193.108.74.209.http: . ack 2215 win 10701 which is the same thing as the FC5 kernel. It took three attempts (killing off the browser and restarting it) to access the website. The retransmission at 19:47:32.451343 looks like quite silly behaviour from the Linux kernel - the remote end has acked data up to 3216 but it's resending old data. Any ideas? -- Russell King -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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