Can anything be done to speed up Roundcube on a Celeron 700 with 512MB RAM (maxed out) running Gentoo Linux? We're using the Chrome browser and the CPU is 95% idle when no one is logged into X. I'm getting reports of 30+ seconds to open an email.
Your problem is likely the amount of RAM; when you start X and Chrome, your client almost surely starts swapping, because there isn't enough RAM for the running processes. Roundcubemail uses AJAX which requires a fast javascript interpreter, and this makes things worse if your processes (including Chrome) are swapping.
On such low-end systems you should use a very lightweight browser instead of Chrome, even if this can give some limitations.
This is simple to check. With all apps running simply run "free -m" and post the output here.
Here's what I get while someone is seated at the system and using Roundcube in Chrome:
# free total used free shared buffers cached Mem: 513072 447812 65260 0 16896 209672 -/+ buffers/cache: 221244 291828 Swap: 2097148 0 2097148
- Grant