from http://www.lstk.net/index.php?id=23

When you running a highload website with PHP-FPM via FastCGI, the following tips may be useful to you : )
1. Compile PHP’s modules as less as possible, the simple the best (fast);
2. Increas PHP FastCGI child number to 100 and even more. Sometime, 200 is OK! ( On 4GB memory server);
3. Using SOCKET PHP FastCGI, and put into /dev/shm on Linux;
4. Increase Linux “max open files”, using the following command (must be root): # echo ‘ulimit -HSn 65536’ >> /etc/profile # echo ‘ulimit -HSn 65536 >> /etc/rc.local # source /etc/profile
5. Increase PHP-FPM open file description rlimit: # vi /path/to/php-fpm.conf Find “1024“ Change 1024 to 4096 or higher number. Restart PHP-FPM.
6. Using PHP code accelerator, e.g eAccelerator, XCache. And set “cache_dir” to /dev/shm on Linux.