Support for SSD
Linux 3.9 brings with it support for Solid State Drives (SSD). The kernel’s Device mapper has a cache target called “dm-cache”, which enables users to set up one drive as a cache for another one. A good example here would be setting up of SSD as cache for an HDD. SSDs can cache the data allowing for faster data writes and when the system is not busy doing much, data can be moved over to slower hard drive. The feature is still labeled experimental but, a new development none the less.

Multiple Sockets listen on Same Port
A new option, SO_REUSEPORT, is now supported by both TCP and UDP sockets allowing them to listen on the same port. This particular approach would help workloads be distributed across all the cores available on the processor. Considering an example, a web server’s processes or threads would be able to open individual sockets to listen on port 80. The kernel will then evenly distribute the connections that come in on this port.

Tom Herbert, a Google developer, developed this extension and further details can be found on an article on

Filesystem Enhancements
The Btrfs filesystem now includes experimental support for RAID 5 and RAID 6 on top of RAID 0 and RAID 1. The reason for having RAID features incorporated within the filesystem is that in the layered approach filesystem and RAID don’t know much about it each other’s internals. In case of failure, entire disk wouldn’t need to be replaced as the kernel will exactly know where a failure has occurred. In contrast the layered approach is not able to access this particular information which meant that the entire volume had to be restored.

Enhanced Graphics Support
Linux 3.9 Kernel now supports Oland graphics chips that are used in 8500 and 8600 Radeon HD Cards. On top of this the kernel also supports AMD Richland APU generation, which is yet to be released. Further the Nouveau driver, meant for the NV40 and NV50 GPUs used on GeForce 6xxx to 9xxx and 1xx to 3xx graphics chips, provides quite a few automatic and manual fan controls.

Drivers, Drivers, Drivers
The Linux 3.9 comes with drivers for Intel’s series 7000 Wi-Fi components; added robustness for HD audio codecs; updates to libata drivers with support for zero power optical device drives (ZPODD); new drivers to support Chromebook from different vendors; driver for Cypress APA I2C trackpads.

3.9’s KVM hypervisor now comes with support for virtualization features of Cortex A15 processors. Beyond this Linux 3.9 kernel’s Xen support now includes drivers for hotplugging processors and memory components. With integration of the drivers for VMware’s VMCI (Virtual Machine Communication Interface) and the VMCI Sockets, Linux 3.9 brings in more support for VMware’s virtualization solutions.

Managing Power
Linux 3.9 brings with it “lightweight suspend” or “suspend freeze” mode allowing the kernel to put all the hardware components to deepest sleep state. The main difference between the suspend-to-RAM (ACPI S3) and this feature is that this particular mode doesn’t power down the components thereby allowing for a quicker resume. Even though the power consumption is higher than that of the suspend-to-RAM, the suspend freeze mode is designed to consume less power than during the normal idle state as the processor will be in a longer and deep sleep. The new mode is ideal for smartphones and tablets that are less responsive suspend-to-RAM state.