PHP Profiling with Cachegrind and XDebug

Often clients ask me to speed up their websites.  In most cases I use a backend to frontend approach. To get a general overview why a website might be slow I usually start by generating a code profile and analyzing it in Wincachegrind/Kcachegrind. This is in my opinion the fastest way to isolate slow code sections.

To generate the code profile you need to have XDebug installed. The following example shows how to install and configure XDebug for Ubuntu. To keep things simple I assume PHP + Apache are already set up and running. In case you are not running Ubuntu you might need to adjust this.

First install the XDebug PHP module:

root@michael:~# apt-get install php5-xdebug

The next step is to configure XDebug (don’t forget to restart Apache after).

/etc/php5/conf.d/xdebug.ini (Ubuntu)


Once this is done add the XDEBUG_PROFILE query string to the URL of the page you want to profile.

XDebug will now generate a code profile in /tmp. In case this doesn’t work double check if Apache has write permissions to the /tmp directory. The file should be called cachegrind.out.[ApacheProcessId]. I do most of my GUI stuff in Windows and use Wincachegrind to visualize my code profiles. Wincachegrind isn’t maintained any more and its last release dates back to 2009, but it still does the trick. Another popular alternative is KCachegrind which provides a neat visual call tree. I prefer Wincachegrind though as it is much easier to follow the code flow. The XDebug profiler documentation page  maintains a full list of alternatives.

Here a screenshot of Wincachegrind visualizing an example code profile.

WinCachegrind profiling session

Note: for security reasons, don’t enable XDebug profiling on live sites. Generating the code profiles is very resource intensive and having profiling enabled might enable an attacker to perform a DOS attack.

PHP Profiling with Cachegrind and XDebug