I've upgraded to WP 3.0 on two Ubuntu-powered virtual hosts recently and both of them experience a problem with runaway CPUs (4xCPU machine and all CPUs crank to 100% usage).
It happens unpredictably 24 to 72 hours after restarting Apache (and thus PHP), so we usually have to wait -days- to experience the failure (one failure only took 6 hours but most happen after at least 48 hours of operation). And the -lack- of failure for 48 hours or more doesn't necessarily mean everything is OK.
Both installs that fail run 15 to 30 plugins, and in both cases we cut back to minimal plugins (12 or so) to try to associate the runaway CPU with some plugin or other. I run 25+ WP instances on about 10 Ubuntu servers and 2 Mac OSX, professionally, so this is not going to be solved by one of the simple solutions like "install WP Super Cache" - this is something much more esoteric and most definitely associated with 3.0.
The installs are -moderate- traffic with 250 to 2000 unique visitors a day. And we don't have the option of turning off -all- plugins to test. The failures -might- be traffic-related because the instance that fails fastest is the one with more traffic.
Both were upgrades from 2.9.2 where we were running reliably without heavy CPU and without restarting Apache except once a week during system upgrades or log rotation. Plugins that are usual high-CPU usage culprits have been trimmed back, PHP code adjusted, or set to proper settings to reduce their CPU usage. Both installs were running with reasonable CPU usage ('top' showing a load around 0.25 or so and CPU load usually around 10%) on WP 2.9.2.
One of the installs we regressed to 2.9.2 yesterday and it is running without a hitch now, so most likely this is a 3.0 problem, but we won't know for another 48 hours or more.
1) I don't see evidence of anyone else experiencing high CPU load related to WP 3.0 - is anyone?
2) Does anyone have experience with a way to -profile- PHP on Linux (Ubuntu) in order to understand what's using the CPU when it goes "hot"?
Current plugin list for the instances that went "hot" most often:
Facebook Like Button for WordPress
Flickr Photo Album
WordPress Database Backup
WP Super Cache
Yet Another Related Posts Plugin