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Message-ID: <CAK6E8=f+TzpX_ZsFpF++1WbBX3iO1iaDcNyYwRXtf0i9Tm6mtQ@mail.gmail.com> Date: Thu, 18 Apr 2013 12:54:48 -0700 From: Yuchung Cheng <ycheng@...gle.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Hagen Paul Pfeifer <hagen@...u.net>, Stephen Hemminger <stephen@...workplumber.org>, David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>, Neal Cardwell <ncardwell@...gle.com>, Tom Herbert <therbert@...gle.com>, Willem de Bruijn <willemb@...gle.com> Subject: Re: [PATCH net-next] tcp: introduce TCPSpuriousRtxHostQueues SNMP counter On Thu, Apr 18, 2013 at 12:29 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > On Thu, 2013-04-18 at 20:19 +0200, Hagen Paul Pfeifer wrote: >> * Eric Dumazet | 2013-04-18 11:06:21 [-0700]: >> >> >On Thu, 2013-04-18 at 10:45 -0700, Stephen Hemminger wrote: >> >> On Thu, 18 Apr 2013 09:52:51 -0700 >> >> Eric Dumazet <eric.dumazet@...il.com> wrote: >> >> >> >> > From: Eric Dumazet <edumazet@...gle.com> >> >> > >> >> > Host queues (Qdisc + NIC) can hold packets so long that TCP can >> >> > eventually retransmit a packet before the first transmit even left >> >> > the host. >> >> Just out of curiosity: do you see effects of commit 9ad7c049 (initRTO from >> 3secs to 1sec) and a long standing queue? (with no path metric, rtt in >> particular) >> > > I have no particular data for the initRTO change. > > Interesting thing is that we send a SYN-ACK for every SYN we receive. > So if a client sends 4 SYN, we'll going to send 4 SYN-ACK, regardless of > the time of last sent SYN-ACK... I am testing a patch to mitigate this exact issue now. Will post soon. > > Here is an interesting study case. > > 12:02:43.484175 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [S], seq 3414870221, win 14600, options [mss 1460,sackOK,TS val 4294775698 ecr 0,nop,wscale 6], length 0 > 12:02:43.484201 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [S.], seq 3173332093, ack 3414870222, win 14480, options [mss 1460,sackOK,TS val 14218683 ecr 4294775698,no > p,wscale 6], length 0 > 12:02:44.884382 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [S.], seq 3173332093, ack 3414870222, win 14480, options [mss 1460,sackOK,TS val 14220084 ecr 4294775698,no > p,wscale 6], length 0 > 12:02:45.470224 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [S], seq 3414870221, win 14600, options [mss 1460,sackOK,TS val 4294776700 ecr 0,nop,wscale 6], length 0 > 12:02:45.470252 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [S.], seq 3173332093, ack 3414870222, win 14480, options [mss 1460,sackOK,TS val 14220669 ecr 4294775698,no > p,wscale 6], length 0 > 12:02:46.762462 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 0 > 12:02:46.762989 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 1:1449, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.763019 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 1449, win 272, options [nop,nop,TS val 14221962 ecr 4294777094], length 0 > 12:02:46.775104 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 1449:2897, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.775138 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 2897, win 317, options [nop,nop,TS val 14221974 ecr 4294777094], length 0 > 12:02:46.787215 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 2897:4345, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.787244 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 4345, win 362, options [nop,nop,TS val 14221986 ecr 4294777094], length 0 > 12:02:46.799326 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 4345:5793, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.799357 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 5793, win 408, options [nop,nop,TS val 14221998 ecr 4294777094], length 0 > 12:02:46.811438 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 5793:7241, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.811465 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 7241, win 453, options [nop,nop,TS val 14222010 ecr 4294777094], length 0 > 12:02:46.823549 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [P.], seq 7241:8689, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.823575 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 8689, win 498, options [nop,nop,TS val 14222023 ecr 4294777094], length 0 > 12:02:46.835662 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 8689:10137, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.835694 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 10137, win 543, options [nop,nop,TS val 14222035 ecr 4294777094], length 0 > 12:02:46.847775 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 10137:11585, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.847801 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 11585, win 589, options [nop,nop,TS val 14222047 ecr 4294777094], length 0 > 12:02:46.859889 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 11585:13033, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.859916 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 13033, win 634, options [nop,nop,TS val 14222059 ecr 4294777094], length 0 > 12:02:46.871998 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], seq 13033:14481, ack 1, win 229, options [nop,nop,TS val 4294777094 ecr 14218683], length 1448 > 12:02:46.872025 IP 7.7.7.84.51407 > 7.7.7.83.49489: Flags [.], ack 14481, win 660, options [nop,nop,TS val 14222071 ecr 4294777094], length 0 > 12:02:49.362204 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], ack 1, win 229, options [nop,nop,TS val 4294778499 ecr 14218683], length 0 > 12:02:50.415265 IP 7.7.7.83.49489 > 7.7.7.84.51407: Flags [.], ack 1, win 229, options [nop,nop,TS val 4294779084 ecr 14218683], length 0 > > We can see the last two packets in this trace being flagged as > TCPSYNChallenge/TCPChallengeACK, because we react to the two extra > SYN-ACK we receive, after queueing the first 10 packets of data. > > > -- 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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