> Alternatively, take your favorite test programs, such as John's, > and make a second pair that reverses the direction the data is > sent. So one pair is server sends, the other is server receives, > try both. That's where we started, BitKeeper, my stripped down test, > and John's test all exhibit the same behavior. And the rsh test > is just a really simple way to demonstrate it. Netperf TCP_STREAM - server receives. TCP_MAERTS (STREAM backwards) - server sends: [root@hpcpc106 ~]# netperf -H 192.168.2.107 TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.2.107 (192.168.2.107) port 0 AF_INET : demo Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 87380 87380 10.17 941.46 [root@hpcpc106 ~]# netperf -H 192.168.2.107 -t TCP_MAERTS TCP MAERTS TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.2.107 (192.168.2.107) port 0 AF_INET : demo Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 87380 87380 10.15 941.35 The above took all the defaults for socket buffers and such. [root@hpcpc106 ~]# uname -a Linux hpcpc106.cup.hp.com 2.6.18-8.el5 #1 SMP Fri Jan 26 14:16:09 EST 2007 ia64 ia64 ia64 GNU/Linux [root@hpcpc106 ~]# ethtool -i eth2 driver: e1000 version: 7.2.7-k2-NAPI firmware-version: N/A bus-info: 0000:06:01.0 between a pair of 1.6 GHz itanium2 montecito rx2660's with a dual-port HP A9900A (Intel 82546GB) in slot 3 of the io cage on each. Connection is actually back-to-back rather than through a switch. I'm afraid I've nothing older installed. sysctl settings attached Where I do have things connected via a switch (HP ProCurve 3500 IIRC, perhaps a 2724) is through the core BCM5704: [root@hpcpc106 netperf2_work]# netperf -H hpcpc107 TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to hpcpc107.cup.hp.com (16.89.84.107) port 0 AF_INET : demo Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 87380 87380 10.03 941.41 [root@hpcpc106 netperf2_work]# netperf -H hpcpc107 -t TCP_MAERTS TCP MAERTS TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to hpcpc107.cup.hp.com (16.89.84.107) port 0 AF_INET : demo Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 87380 87380 10.03 941.37 [root@hpcpc106 netperf2_work]# ethtool -i eth0 driver: tg3 version: 3.65-rh firmware-version: 5704-v3.27 bus-info: 0000:01:02.0 rick jones