Anyone maybe know is there Linux (debian) tool for testing PHP application performance? I want to check in witch places my PHP/MySQL script need optimization.
If you want to profile your scripts and tweak performance under test conditions, have a look at xdebug.
For HTTP optimization, you could do a lot worse than firebug.
However that does not replace the need to tune the application as a whole - if you've got a script taking 30 seconds to complete which only gets run once a month - then its less of a priority then one which takes 5 seconds and is fired of 1000 times per hour.
AFAIK there's no free off-the-shelf solution - I added %D to my apache logs and use some custom code around that to identify problems areas (prioritized based on product of frequency and duration for each URL). I also use a modified version of this mysql log parser for my SQL code.
There are commercial offerings - but