WebSphere Peformance - Alexandre Polozoff's Point of View
One of my colleagues came across an interesting performance problem on Linux. Due to the Linux Completely Fair Schedule it affects Java's performance. Read the link and see if you're having a problem. This was on RHEL 5.6 Kernel 2.6.18.
The popular XC10 appliance has periodic firmware upgrades. However, a recent client was experiencing slower response times from the XC10 running with a recent firmware upgrade. After much looking we saw in the AIX client and XC10 packet traces that the ACK from the AIX client was taking 200ms on almost every response from the XC10. This anomaly can be remedied by setting on AIX
no -o -o tcp_nodelayack=1
The topic gets into interesting TCP/IP conversations about Nagle algorithms, MTU, piggybacking ACKs on data packets and timeouts that I was not aware of but the AIX level TCP/IP configuration change resolved the problem. A similar setting exists for Linux (see techrepublic link below) Note: this can increase the number of packets on the network however in our testing after making the change we did not see that side effect. However, collect the necessary tcpdump/iptrace to trust and verify.
Edit Nov 20 to add some references and interesting related reading