As you may know, iXit overlay for Gentoo offers MultiPath TCP support for well tested Gentoo kernel 3.11.10 with MPTCP patchset from stable branch 0.88.
Since today, you may find new mptcp-sources, based on 3.12.2 kernel with MPTCP patchset from trunk branch. It’s lightly tested. No regression found for our systems.
Enjoy tuned 3.12 kernel, it should provide improved TCP stack and better performance for modern AMD GPUs.