Kernel configurations

[New User]

Hi,

I am new to LVS, I have spent numerous days pouring over the various documentations and mailing list. I have mostly decided to deploy HA LVS-NAT on CentOS (but with a fresh kernel 2.6.18.1) with keepalived. These will be dedicated machines to load balancing with 2G RAM.

I am in the process of building out the system, but my usage is more focused on maximizing number of connections than maximum throughput in terms of Mb/s or Gb/s. The connection rate is hundreds of thousand connections per second (even million+). The connections will be both TCP and UDP. TCP connections are very short lived, and the requests and responses are very small, mostly no larger than the TCP and UDP header.

I would like to know the optimal kernel configurations for my setup:

Hash table size - The document offers conflict recommendations. It first emphasis NOT to change it and leave it at 12, which is 4096 buckets. But it goes on explaining a scenario where there are 200 connections/second with each connection maintaining 200 seconds, the hash table size should be 15. If this implementation is similar to Netfilter's conn_track, then there should be benefits in increasing the number of buckets. Statistically speaking, this can reduce number of traverse in the linked list within the bucket. Assuming everything is even distributed, then double the number of buckets, it should half the number of entries in the linked list. Of course, this comes at an expense of extra memory requirement when connection number is low. So is there any other negative impacts (especially at performance) in increasing this number?

Preemptive option - Although this may not be directly related to LVS, but with 2.6 kernel, one can set preemptive option. Does one gain/loss performance when the machine is dedicated to LVS, which is only network I/O intensive?

SMP - It is also recommended not to use SMP because of spinlocks. However, given most of machines are multi-core, and large network traffic with many small packets also causes a lot of interrupts. In this situtation, is it still better not to use SMP?

I appreciate any recommendations in advance.