Linux Source Dedicated Server on FreeBSD

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=434

If you would like to run the Linux Source Dedicated Server on your FreeBSD machine, you will need to compile your kernel with the CPU_ENABLE_SSE option to ensure your machine’s MMX capabilities are recognized by the kernel.

In addition to the CPU_ENABLE_SSE option, some machines may require that the CPU_ATHLON_SSE_HACK option be enabled when compiling the kernel.