Linus Torvalds recently released a new version of the Linux kernel — version 3.9 — that advances the core of the GNU/Linux operating system with a number of new features. Among other tweaks, the new kernel rolls in new drivers, improves virtualization support, adds new hardware sleep modes, and tweaks file system and storage support.
The new kernel has added quite a few new experimental features, but developers/enthusiasts will no longer have to employ the CONFIG_EXPERIMENTAL flag when compiling the kernel in order to enable them. The kernel development team has decided to remove that option, enable the features by default, and merely tag those experimental features in the documentation. One of the experimental features is SSD caching that allows a solid state drive to cache both reads and writes. The SSD can cache frequently accessed data on the faster solid state drive as well as take the write cached data and write it to the hard drive when the IO subsystem isn’t being heavily utilized. The feature is not new to Linux distributions, but the caching support has now been moved to the kernel. Furthermore, the kernel is now RAID-aware when using the btrfs file system and RAID 5 or RAID 6.
On the driver front, Linux Kernel 3.9 now supports Intel’s upcoming 802.11ac Wi-Fi adapters, improved HD audio codec, AMD’s Oland (8500/8600) and Richland GPUs, and additional NVIDIA GPU support. The new kernel also rolls in a power-optimized driver for Intel’s Haswell GPU and several more track pads.
Kernel 3.9 also adds a new suspend/sleep mode. It will use more power than the traditional S3 (suspend to memory) sleep mode because components are not completely powered down (merely at their lowest sleep mode), but the system will be almost-instantly accessible upon exiting the new suspend mode as a result. According to H-Online, this "lightweight suspend" mode would be ideal for mobile devices or hardware used in network appliances. Also interesting is support for a KVM hypervisor on ARM Cortex A15 SoCs as well as some software tweaks to the kernel to improve web server workloads by allowing multiple networking sockets (and associated CPU processes) to listen on the same network port.
In all, version 3.9 looks to be a worthy upgrade, and one that I hope Linux distro makers will opt for in upcoming releases. I think the new drivers and the SSD caching being rolled into the kernel are the most important features for desktop users, though the networking stack improvements also sound interesting.
For more details, Thorsten Leemhuis has written up an extensive article on the new kernel.