netdev - Re: [PATCH v2 net-next] tcp: TSO packets automatic sizing

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Date:	Mon, 26 Aug 2013 13:28:09 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Van Jacobson <vanj@...gle.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH v2 net-next] tcp: TSO packets automatic sizing

On Mon, 2013-08-26 at 12:09 -0700, Yuchung Cheng wrote:

> init write of 10MSS now looks good, but the delay still shows up if 9
> < write-size < 10 MSS...
> 
> I use packetdrill to do write(14599) bytes of MSS 1460
> 
> 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> 0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> 0.000 bind(3, ..., ...) = 0
> 0.000 listen(3, 1) = 0
> 
> 0.100 < S 299245565:299245565(0) win 32792 <mss
> 1460,sackOK,nop,nop,nop,wscale 7>
> 0.100 > S. 0:0(0) ack 299245566 <mss 1460,nop,nop,sackOK,nop,wscale 6>
> 0.200 < . 1:1(0) ack 1 win 257
> 0.200 accept(3, ..., ...) = 4
> +.000 write(4, ..., 13141) = 13141
> +3 %{ print "done" }%
> 
> and tcpdump shows
> 
> 31.819958 IP cli > srv: S 299245565:299245565(0) win 32792 <mss 1460,sackOK,nop,
> nop,nop,wscale 7>
> 000034 IP srv > cli: S 203810874:203810874(0) ack 299245566 win 29200
> <mss 1460,nop,nop,sackOK,nop,wscale 6>
> 099966 IP cli > srv: . ack 1 win 257
> 000079 IP srv > cli: . 1:2921(2920) ack 1 win 457
> 000010 IP srv > cli: . 2921:5841(2920) ack 1 win 457
> 000005 IP srv > cli: . 5841:8761(2920) ack 1 win 457
> 000004 IP srv > cli: . 8761:11681(2920) ack 1 win 457
> 199659 IP srv > cli: . 11681:13141(1460) ack 1 win 457
> ...

It works correctly here, I wonder what's happening on your host.

lpq83:~# tcpdump -p -n -s 0 -i any port 8080 -ttt
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
000000 IP 192.0.2.1.42148 > 192.168.0.1.8080: S 299245565:299245565(0) win 32792 <mss 1460,sackOK,nop,nop,nop,wscale 7>
000042 IP 192.168.0.1.8080 > 192.0.2.1.42148: S 223873324:223873324(0) ack 299245566 win 29200 <mss 1460,nop,nop,sackOK,nop,wscale 6>
099946 IP 192.0.2.1.42148 > 192.168.0.1.8080: . ack 1 win 257
000087 IP 192.168.0.1.8080 > 192.0.2.1.42148: . 1:2921(2920) ack 1 win 457
000006 IP 192.168.0.1.8080 > 192.0.2.1.42148: . 2921:5841(2920) ack 1 win 457
000004 IP 192.168.0.1.8080 > 192.0.2.1.42148: . 5841:8761(2920) ack 1 win 457
000004 IP 192.168.0.1.8080 > 192.0.2.1.42148: . 8761:11681(2920) ack 1 win 457
000005 IP 192.168.0.1.8080 > 192.0.2.1.42148: . 11681:13141(1460) ack 1 win 457
000002 IP 192.168.0.1.8080 > 192.0.2.1.42148: P 13141:13142(1) ack 1 win 457


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