SMP and 2.6 kernel perfomance issue

Hello group,

when we upgrade from kernel version 2.4.20 to the kernel 2.6.10 we notice substantial performance degradation when running our multi process benchmark. After quite intensive analysis we found that problem must be related to the SMP. If we disable SMP when configuring kernel we get the same results with both kernel versions. With SMP enabled 2.6.10 kernel performs much worse than 2.4.20.

Results of the benchmark (bigger numbers are better)

kernel 2.4.20 (SMP ON) 2845 kernel 2.6.10 (SMP ON) 543 kernel 2.6.10 (SMP OFF),kernel 2.4.20 (SMP OFF) 1626

Any comments or suggestions are more than welcome.

Sani

Additional observation is related to the CPU utilization - when running benchmark on the 2.4.20 we were able to utilize all CPUs 100%, now with 2.6.10 we can achieve just 35 % utilization (according to top).

HW platform is Intel server blade with two Xeon processors.

SW benchmark is as follows: - nine processes are created, all equal priorities. Process 1. sends message to the process 2. which waits on message receive, proc 2. receives message from proc 1, sends message to proc 3, waits again on message receive, proc 3 receives message from proc 2, sends it to proc 4. .... and so on until we reach proc 9, which sends message back to proc 8, which sends message back to proc 7 ... and so on until proc 1 where whole procedure is repeated. For benchmark we create four such chains to run independently in parallel (four times nine processes). Upper numbers represent how many repebreastion we achieve per second.