Evaluating the FreeBSD 9.x modular congestion control framework's performance impact

Modular congestion control (modCC) is a recently added feature to the FreeBSD kernel. The implementation introduced a number of key changes to the TCP stack with the potential to impact performance. We test the relative performance of TCP before and after these changes using the 215163 and 217806 Subversion repository revisions of FreeBSD's ''head'' (9.x) development branch respectively.We find that the modCC changes do not adversely impact performance on the whole, and in fact slightly improve the nett performance of the FreeBSD TCP stack.