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Date:      Mon, 21 Oct 2013 13:58:17 -0700
From:      Colin Percival <cperciva@freebsd.org>
To:        Andre Oppermann <andre@freebsd.org>, Julian Elischer <julian@freebsd.org>, freebsd-net@freebsd.org
Subject:   Re: LRO causing stretch ACK violations interacts badly with delayed ACKing
Message-ID:  <52659569.8090301@freebsd.org>
In-Reply-To: <52658A79.6070705@freebsd.org>
References:  <52605EC9.6090406@freebsd.org> <526478D0.1000601@freebsd.org> <5264869E.4000308@freebsd.org> <5265450C.1060601@freebsd.org> <526558D2.3010505@freebsd.org> <52658726.4030106@freebsd.org> <52658A79.6070705@freebsd.org>

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On 10/21/13 13:11, Andre Oppermann wrote:
> On 21.10.2013 21:57, Andre Oppermann wrote:
>> This is an excellent observation!  Our tcp doesn't know about LRO
>> and I prepared the mbuf header to carry information about the number
>> of merged LRO segments.  That's not done yet again.  However a small
>> heuristic in tcp_input looking for segment > mss should be sufficient
>> for now.  Let me have a look at patching it into a suitable place.
> 
> Please check out the patch below.  Haven't tested it myself yet though.

Yes, this works:
> 00:00:00.000000 IP 10.148.229.78.24405 > 176.32.98.166.443: Flags [S], seq 3220740500, win 65535, options [mss 1460,nop,wscale 6,sackOK,TS val 350742 ecr 0], length 0
> 00:00:00.000613 IP 176.32.98.166.443 > 10.148.229.78.24405: Flags [S.], seq 1783557911, ack 3220740501, win 8190, options [mss 1460,nop,wscale 6], length 0
> 00:00:00.000657 IP 10.148.229.78.24405 > 176.32.98.166.443: Flags [.], ack 1, win 1026, length 0
> 00:00:00.001842 IP 176.32.98.166.443 > 10.148.229.78.24405: Flags [.], ack 1, win 127, length 0
> 00:00:00.032269 IP 10.148.229.78.24405 > 176.32.98.166.443: Flags [P.], seq 1:318, ack 1, win 1026, length 317
> 00:00:00.033080 IP 176.32.98.166.443 > 10.148.229.78.24405: Flags [.], ack 318, win 108, length 0
> 00:00:00.033115 IP 176.32.98.166.443 > 10.148.229.78.24405: Flags [.], seq 1:4097, ack 318, win 108, length 4096
> 00:00:00.033129 IP 10.148.229.78.24405 > 176.32.98.166.443: Flags [.], ack 4097, win 962, length 0

Please commit this fix and get it merged for 10.0-RELEASE!

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid




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