From: Ben Greear <greearb@candelatech•com>
To: rick.jones2@hp•com
Cc: Stephen Hemminger <shemminger@vyatta•com>,
netdev <netdev@vger•kernel.org>
Subject: Re: TCP funny-ness when over-driving a 1Gbps link (and wifi)
Date: Fri, 20 May 2011 14:33:16 -0700 [thread overview]
Message-ID: <4DD6DE1C.8090607@candelatech.com> (raw)
In-Reply-To: <4DD5E270.3030209@candelatech.com>
On 05/19/2011 08:39 PM, Ben Greear wrote:
> On 05/19/2011 05:46 PM, Rick Jones wrote:
>> On Thu, 2011-05-19 at 17:37 -0700, Ben Greear wrote:
>>> On 05/19/2011 05:24 PM, Rick Jones wrote:
>>>>>>> [root@i7-965-1 igb]# netstat -an|grep tcp|grep 8.1.1
>>>>>>> tcp 0 0 8.1.1.1:33038 0.0.0.0:* LISTEN
>>>>>>> tcp 0 0 8.1.1.1:33040 0.0.0.0:* LISTEN
>>>>>>> tcp 0 0 8.1.1.1:33042 0.0.0.0:* LISTEN
>>>>>>> tcp 0 9328612 8.1.1.2:33039 8.1.1.1:33040 ESTABLISHED
>>>>>>> tcp 0 17083176 8.1.1.1:33038 8.1.1.2:33037 ESTABLISHED
>>>>>>> tcp 0 9437340 8.1.1.2:33037 8.1.1.1:33038 ESTABLISHED
>>>>>>> tcp 0 17024620 8.1.1.1:33040 8.1.1.2:33039 ESTABLISHED
>>>>>>> tcp 0 19557040 8.1.1.1:33042 8.1.1.2:33041 ESTABLISHED
>>>>>>> tcp 0 9416600 8.1.1.2:33041 8.1.1.1:33042 ESTABLISHED
>>>>>>
>>>>>> I take it your system has higher values for the tcp_wmem value:
I tried a different test today: 3 TCP connections between two
wifi station interfaces (using ath9k). Each connection is
endpoint configured to send 100Mbps of traffic to the peer.
With a single connection, it does OK (maybe 250ms round-trip time max).
With 3 of them running, round-trip user-space to user-space latency
often goes above 3 seconds.
I had set tcp_wmem smaller for this test, and I verified that
the socket SND/RCV buffer setsockopt was not being called.
[root@lec2010-ath9k-1 lanforge]# netstat -an|grep tcp|grep 33
tcp 0 0 12.12.12.4:33040 0.0.0.0:* LISTEN
tcp 0 0 12.12.12.4:33042 0.0.0.0:* LISTEN
tcp 0 0 12.12.12.4:33044 0.0.0.0:* LISTEN
tcp 0 556072 12.12.12.4:33040 12.12.12.3:33039 ESTABLISHED
tcp 0 274916 12.12.12.3:33043 12.12.12.4:33044 ESTABLISHED
tcp 0 0 192.168.100.138:33738 192.168.100.3:2049 ESTABLISHED
tcp 0 205156 12.12.12.4:33042 12.12.12.3:33041 ESTABLISHED
tcp 0 217184 12.12.12.3:33041 12.12.12.4:33042 ESTABLISHED
tcp 0 436552 12.12.12.3:33039 12.12.12.4:33040 ESTABLISHED
tcp 0 288820 12.12.12.4:33044 12.12.12.3:33043 ESTABLISHED
[root@lec2010-ath9k-1 lanforge]# cat /proc/sys/net/ipv4/tcp_wmem
4096 16384 4000000
This is 2.6.39-wl+ kernel.
So, seems a general issue with over-driving links with multiple TCP connections.
Doesn't seem like a regression, and probably not really a bug, but maybe the
buffer-bloat project will help this sort of thing...
Thanks,
Ben
--
Ben Greear <greearb@candelatech•com>
Candela Technologies Inc http://www.candelatech.com
next prev parent reply other threads:[~2011-05-20 21:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-19 22:47 TCP funny-ness when over-driving a 1Gbps link Ben Greear
2011-05-19 23:18 ` Stephen Hemminger
2011-05-19 23:20 ` Ben Greear
2011-05-19 23:42 ` Ben Greear
2011-05-20 0:05 ` Rick Jones
2011-05-20 0:12 ` Ben Greear
2011-05-20 0:24 ` Rick Jones
2011-05-20 0:37 ` Ben Greear
2011-05-20 0:46 ` Rick Jones
2011-05-20 3:39 ` Ben Greear
2011-05-20 21:33 ` Ben Greear [this message]
2011-05-26 15:28 ` TCP funny-ness when over-driving a 1Gbps link (and wifi) Chris Friesen
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