[RndTbl] Network performance tuning

[Kevin McGregor]

Well. I plugged in my iMac (Intel, Core 2 Duo T7200, 2.00 GHz) to my gigabit
switch and ran iperf on it in server and client mode. The only copy I could
find for download (executable) was 1.70, and was compiled for the PowerPC
Macs. Here are the results between the iMac and my server:

$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 192.168.27.10 port 5001 connected with 192.168.27.29 port 49371
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-20.0 sec  2.17 GBytes    930 Mbits/sec

$ iperf -t 20 -c 192.168.27.29
------------------------------------------------------------
Client connecting to 192.168.27.29, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.27.10 port 44201 connected with 192.168.27.29 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-20.0 sec  2.18 GBytes    936 Mbits/sec

The server and the iMac seem pretty happy to talk to each other -- that's
twice the performance of any other TCP result I've had! Just as a check, I
plugged the PC into the same cable as the iMac had been plugged into:

$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 192.168.27.10 port 5001 connected with 192.168.27.23 port 4701
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-20.0 sec    386 MBytes    162 Mbits/sec

Much lower results. It seems to me that the problem is with the network
hardware or TCP/IP stack on the PC side. Does anyone else want to venture an
opinion? Or another test to run?

Kevin

On Wed, Apr 7, 2010 at 4:11 PM, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> On 2010-04-07 Adam Thompson wrote:
> > Actually, I was mainly hoping to verify that it was, indeed, a
> > hardware problem.  One person (Trevor) reporting similar results has
> > fairly decent-quality GigE NICs on both sides – or at least what I
> > *assumed* to be fairly decent-quality NICs!
>
> I should hope so, my NICs are Intel server grade gigabit on the server
> and Intel high-end workstation grade gigabit on the client ($100-$300
> NICs, retail).
>
> Kevin, I didn't have time to scan your exact results, is it mostly
> pc->server that's slow or server<-pc?  And your pc is Windows, I gather
> (XP?).
>
> My big problem has always been windows->linux performance (but never
> linux->windows).  I've given up on it for now, but one thing that made
> a HUGE difference was turning OFF jumbo packets.  I instantly got 5X
> better performance with jumbo OFF.  Yes, my switch is jumbo capable,
> and it was enabled, and set properly on the pc and linux.  Go figure.
> I blame the Linksys WebSmart switch, but who knows.
>
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