From: Ben Greear <greearb@candelatech.com>
To: Stephen Hemminger <shemminger@vyatta.com>
Cc: netdev <netdev@vger.kernel.org>
Subject: Re: TCP funny-ness when over-driving a 1Gbps link.
Date: Thu, 19 May 2011 16:42:52 -0700 [thread overview]
Message-ID: <4DD5AAFC.8070509@candelatech.com> (raw)
In-Reply-To: <4DD5A5CD.7040303@candelatech.com>
On 05/19/2011 04:20 PM, Ben Greear wrote:
> On 05/19/2011 04:18 PM, Stephen Hemminger wrote:
>> If you overdrive, TCP expects your network emulator to have
>> a some but limited queueing (like a real router).
>
> The emulator is fine, it's not being over-driven (and has limited
> queueing if it was
> being over-driven). The queues that are backing up are in the tcp
> sockets on the
> sending machine.
>
> But, just to make sure, I'll re-run the test with a looped back cable...
Well, with looped back cable, it isn't so bad. I still see a small drop
in aggregate throughput (around 900Mbps instead of 950Mbps), and
latency goes above 600ms, but it still performs better than when
going through the emulator.
At 950+Mbps, the emulator is going to impart 1-2 ms of latency
even when configured for wide-open.
If I use a bridge in place of the emulator, it seems to settle on
around 450Mbps in one direction and 945Mbps in the other (on the wire),
with round-trip latencies often over 5 seconds (user-space to user-space),
and a consistent large chunk of data in the socket send buffers:
[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
Thanks,
Ben
--
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
next prev parent reply other threads:[~2011-05-19 23:42 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 [this message]
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 ` TCP funny-ness when over-driving a 1Gbps link (and wifi) Ben Greear
2011-05-26 15:28 ` Chris Friesen
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