Here's a look at the performance of the Linux 3.4 kernel, which was recently released, compared to all major kernel releases going back to Linux 2.6.39. Multiple kernel sub-systems are being compared in this round of Intel Linux benchmarking.
While there's a lot of tests to go through, overall the testing was quite simple and came down to testing Ubuntu 12.04 LTS x86_64 when swapping out the mainline Linux kernel releases from 2.6.39 through 3.4.
From a Lenovo ThinkPad W510 notebook with an Intel Core i7 720QM CPU, 160GB Intel SSD, and NVIDIA Quadro FX 880M graphics, the Linux 2.6.39, 3.0, 3.1, 3.2, 3.3, and 3.4 Git kernels were obtained from the Ubuntu mainline kernel package repository. All settings were left at their defaults between tests.
In terms of the features and changes for this latest Linux kernel stable update, see the Phoronix Linux 3.4 kernel articles.