Tuning for CPU usage

[alex]

We are running into a definite CPU bottleneck, the IO and memory seem to be holding up fine. Are there any specific settings that can be tweaked to improve this?

[mistwang]

lshttpd should consumes little CPU cycles, the rest should be taken by PHP processes. So, you need to focus on PHP tuning, like using opcode caching if it has not been used yet. Also, try finding vBulltin add-on modules which can improve performance.
Worst case, add more hardware. :-) Our load balancer will be ready soon.

[ts77]

just curious:
where will the load-balancer kick in? separate software in front of a couple of lsws servers or simply included in them?

[xing]

alex, based on your last php.ini configuration, you should think about using op-code caching like mistwang suggested. For php 4 code, I would highly recommend eacclerator.co.uk. Note when installing, make sure you disable "code optimization", only enable the caching part of eAcc.

Opcode caching can drastically improve php's cpu usage.

Another sure thing is also to upgrade to the latest vBulletin build.

[mistwang]

ts77,

The load balancer is a standalone server in front of a web server farm.

[alex]

Eaccelerator worked...oh my god did it work

[ts77]

alex, any measures of that?

[alex]

Prior to installing eaccelerator last night top was showing 100 (where they were set to give a "server too busy" message). This was happening at about 2200 simultaneous users.
Today we made it to 2450 users, I never saw load go over 40 and most of the time it was around 20-30

[Xorlev]

I recommend APC over Eaccelerator, but eh, if it works. Even so with such concurrency it'd be recommended to upgrade to a more powerful server. I'd recommend an Opteron, as they're rather leading the server market in price/performance ratio.