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Message-ID: <AANLkTin0soTsGJIqNVYp32AFf-H9I3yY9xHI1rgYBIVW@mail.gmail.com>
Date:	Thu, 3 Jun 2010 17:05:07 -0700
From:	Ivan Novick <novickivan@...il.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	netdev@...r.kernel.org
Subject: Re: 200 millisecond timeouts in TCP

On Thu, Jun 3, 2010 at 4:10 PM, Hagen Paul Pfeifer <hagen@...u.net> wrote:
> * Ivan Novick | 2010-06-03 15:37:24 [-0700]:
>
>>Using tcpdump and systemtap I am seeing that sometimes retransmission
>>of data is sent after waiting 200 milliseconds.  However sometimes
>>retransmissions happen quicker.
>
> Quicker as 200ms? Conservatively the minimum TCP RTO should be 1s (rfc2988),
> Linux differs from this default and define the minimum RTO to 200ms:
>
> #define TCP_RTO_MIN     ((unsigned)(HZ/5))
>
> Can you post the tcpdump traces where the relevant retransmission is recognizable?
Here is the tcpdump, below.
Cheers,
Ivan Novick

tcpdump on machine dell-s1-1:
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168771588:168787516(15928) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000052 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168749868 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000086 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168754212 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000026 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168757108 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000040 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168762900 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000013 IP dell-s1-1.46799 > dell-s2-1.47500: .
168787516:168803444(15928) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000046 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168768692 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000059 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168775932 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000006 IP dell-s1-1.46799 > dell-s2-1.47500: .
168803444:168817924(14480) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000049 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168781724 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000444 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168786068 win 16200
<nop,nop,timestamp 2077240629 1375977402>
000025 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168804892}>
000020 IP dell-s1-1.46799 > dell-s2-1.47500: .
168817924:168819372(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168806340}>
000006 IP dell-s1-1.46799 > dell-s2-1.47500: .
168819372:168820820(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168809236}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168820820:168822268(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168812132}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168822268:168823716(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168815028}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168823716:168825164(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000005 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168817924}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168825164:168826612(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000412 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168819372}>
000007 IP dell-s1-1.46799 > dell-s2-1.47500: .
168787516:168788964(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168822268}>
000004 IP dell-s1-1.46799 > dell-s2-1.47500: .
168788964:168790412(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168825164}>
000003 IP dell-s1-1.46799 > dell-s2-1.47500: .
168790412:168791860(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168826612}>
000004 IP dell-s1-1.46799 > dell-s2-1.47500: .
168791860:168793308(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000383 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168788964 win 16188
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000006 IP dell-s1-1.46799 > dell-s2-1.47500: .
168793308:168794756(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168790412 win 16177
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000004 IP dell-s1-1.46799 > dell-s2-1.47500: .
168794756:168796204(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240629>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168793308 win 16154
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168796204:168797652(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240629>
000132 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168794756 win 16143
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168797652:168799100(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000018 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168797652 win 16120
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000006 IP dell-s1-1.46799 > dell-s2-1.47500: .
168799100:168800548(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000198 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168799100 win 16109
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000006 IP dell-s1-1.46799 > dell-s2-1.47500: .
168800548:168801996(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000024 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168800548 win 16098
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000007 IP dell-s1-1.46799 > dell-s2-1.47500: .
168826612:168828060(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
203979 IP dell-s1-1.46799 > dell-s2-1.47500: .
168800548:168801996(1448) ack 1 win 46 <nop,nop,timestamp 1375977608
2077240630>
000110 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168828060 win 16200
<nop,nop,timestamp 2077240834 1375977404,nop,nop,sack 1
{168800548:168801996}>

tcpdump on machine dell-s2-1:

000032 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168746972 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000022 IP dell-s1-1.46799 > dell-s2-1.47500: .
168746972:168748420(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240627>
000023 IP dell-s1-1.46799 > dell-s2-1.47500: .
168748420:168749868(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240627>
000013 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168749868 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000037 IP dell-s1-1.46799 > dell-s2-1.47500: .
168749868:168751316(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240627>
000027 IP dell-s1-1.46799 > dell-s2-1.47500: .
168751316:168754212(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240627>
000021 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168754212 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000005 IP dell-s1-1.46799 > dell-s2-1.47500: .
168754212:168755660(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240627>
000002 IP dell-s1-1.46799 > dell-s2-1.47500: .
168755660:168757108(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000004 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168757108 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000019 IP dell-s1-1.46799 > dell-s2-1.47500: .
168757108:168760004(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000026 IP dell-s1-1.46799 > dell-s2-1.47500: .
168760004:168762900(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000011 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168762900 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000014 IP dell-s1-1.46799 > dell-s2-1.47500: .
168762900:168765796(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000026 IP dell-s1-1.46799 > dell-s2-1.47500: .
168765796:168768692(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000011 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168768692 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000016 IP dell-s1-1.46799 > dell-s2-1.47500: .
168768692:168773036(4344) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000026 IP dell-s1-1.46799 > dell-s2-1.47500: .
168773036:168775932(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000017 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168775932 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000008 IP dell-s1-1.46799 > dell-s2-1.47500: .
168775932:168778828(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000025 IP dell-s1-1.46799 > dell-s2-1.47500: .
168778828:168781724(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000012 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168781724 win 16200
<nop,nop,timestamp 2077240628 1375977402>
000014 IP dell-s1-1.46799 > dell-s2-1.47500: .
168781724:168784620(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000024 IP dell-s1-1.46799 > dell-s2-1.47500: .
168784620:168786068(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000025 IP dell-s1-1.46799 > dell-s2-1.47500: .
168786068:168787516(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000091 IP dell-s1-1.46799 > dell-s2-1.47500: .
168801996:168804892(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000009 IP dell-s1-1.46799 > dell-s2-1.47500: .
168804892:168806340(1448) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000026 IP dell-s1-1.46799 > dell-s2-1.47500: .
168806340:168809236(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000027 IP dell-s1-1.46799 > dell-s2-1.47500: .
168809236:168812132(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000024 IP dell-s1-1.46799 > dell-s2-1.47500: .
168812132:168815028(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000029 IP dell-s1-1.46799 > dell-s2-1.47500: .
168815028:168817924(2896) ack 1 win 46 <nop,nop,timestamp 1375977402
2077240628>
000077 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168786068 win 16200
<nop,nop,timestamp 2077240629 1375977402>
000006 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168804892}>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168806340}>
000001 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168809236}>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168812132}>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168815028}>
000001 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168817924}>
000203 IP dell-s1-1.46799 > dell-s2-1.47500: .
168817924:168819372(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000028 IP dell-s1-1.46799 > dell-s2-1.47500: .
168819372:168822268(2896) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000025 IP dell-s1-1.46799 > dell-s2-1.47500: .
168822268:168825164(2896) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000024 IP dell-s1-1.46799 > dell-s2-1.47500: .
168825164:168826612(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000312 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168819372}>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168822268}>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168825164}>
000002 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168787516 win 16200
<nop,nop,timestamp 2077240629 1375977402,nop,nop,sack 1
{168801996:168826612}>
000074 IP dell-s1-1.46799 > dell-s2-1.47500: .
168787516:168788964(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000013 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168788964 win 16188
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000013 IP dell-s1-1.46799 > dell-s2-1.47500: .
168788964:168790412(1448) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000013 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168790412 win 16177
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000014 IP dell-s1-1.46799 > dell-s2-1.47500: .
168790412:168793308(2896) ack 1 win 46 <nop,nop,timestamp 1375977403
2077240629>
000015 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168793308 win 16154
<nop,nop,timestamp 2077240629 1375977403,nop,nop,sack 1
{168801996:168826612}>
000333 IP dell-s1-1.46799 > dell-s2-1.47500: .
168793308:168794756(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240629>
000016 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168794756 win 16143
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000010 IP dell-s1-1.46799 > dell-s2-1.47500: .
168794756:168797652(2896) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240629>
000013 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168797652 win 16120
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000111 IP dell-s1-1.46799 > dell-s2-1.47500: .
168797652:168799100(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000021 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168799100 win 16109
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000004 IP dell-s1-1.46799 > dell-s2-1.47500: .
168799100:168800548(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168800548 win 16098
<nop,nop,timestamp 2077240630 1375977404,nop,nop,sack 1
{168801996:168826612}>
000258 IP dell-s1-1.46799 > dell-s2-1.47500: .
168800548:168801996(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000036 IP dell-s1-1.46799 > dell-s2-1.47500: .
168826612:168828060(1448) ack 1 win 46 <nop,nop,timestamp 1375977404
2077240630>
000030 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168826612 win 16077
<nop,nop,timestamp 2077240630 1375977404>
000003 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168828060 win 16066
<nop,nop,timestamp 2077240630 1375977404>
203890 IP dell-s1-1.46799 > dell-s2-1.47500: .
168800548:168801996(1448) ack 1 win 46 <nop,nop,timestamp 1375977608
2077240630>
000042 IP dell-s2-1.47500 > dell-s1-1.46799: . ack 168828060 win 16200
<nop,nop,timestamp 2077240834 1375977404,nop,nop,sack 1
{168800548:168801996}>
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