Hello Hans,
Thanks for the great info Replies below:
If you can change settings on your server...
I can't. Shared host.
The building of the cache takes a bit of time and consumes CPU also of course. It also all depends whats your ratio of logged in and anonymous users (you can see this easily in admin menu). If your problem with CPU comes from a lot of logged in users
Where can I find this ratio? The best I've found is the list of top visitors in the past 3 days. It looks like anonymous visitors dominate.
Make sure you disabled and uninstalled all modules which you don't use. Reduce number of cron runs and backups.
I disabled one module, but not much. Cron jobs are only once a day, in the morning, and backups are done by the host.
Try to see where the load comes from. Search and views (especially views with relationships) can be heavy consumers.
Hmm... I do have search and views. I'll take a closer look at those. I think I can probably do without the views.
A radical but very effective solution for reducing CPU is to install http://drupal.org/project/boost it makes a static pure html copy of your pages. I'm using it on a few sites with great success, page loads dropped to 0.3s for anonymous users and also server load decreased with factor between 5 and 10.
Thanks. I'll take a closer look. Is there any drawback to making static pages? Can you edit the pages later? Why doesn't everybody use this?
css aggregation is very good for loading speed performance; I'm not sure about the exact influence on cpu but I expect its not of much influence so I would put it on.
Ok, I've added it.
Wim Leers has a very interesting article on page loading performance: http://wimleers.com/article/improving-drupals-page-loading-performance
Thanks!
Daniel.