Chris Mason sent in the Btrfs pull request today for the Linux 3.13 kernel. The changes for this release cyclce include the "usual merge window set of bug fixes, performance improvements and cleanups." Chris though was quick to point out there's some really nice optimizations for Btrfs write-back performance by kernel developer Miao Xie.
There's about 80 commits and close to three thousand lines of code that has been changed for the Btrfs file-system in Linux 3.13. More details on the Btrfs specifics for 3.13 can be found via the pull request.
New Btrfs, XFS, EXT4, and F2FS file-system benchmarks from the Linux 3.13 kernel on SSD/HDD storage will come shortly after the release of 3.13-rc1.