Linux 3.9 kernel release offers SSD caching and server performance improvements

The Linux 3.9 kernel brings with it an SSD caching, improved performance for multi-threaded network server applications and a host of other features.
Written by Nick Heath, Contributor

The latest version of the Linux kernel has been released – bringing with it support for SSD caching and a performance boost for some server workloads.

The 3.9 release, made available by Linus Torvalds on Sunday, offers various performance enhancements, new features and additional driver support.

SSD caching

SSDs or other storage devices will be able to be used as a cache for a hard drive, potentially speeding up data writes and reads. The ability to use SSDs as a cache comes courtesy of changes to the Device Mapper, which now includes a cache target called "dm-cache".

Server performance

Performance of multi-threaded network server applications running on multi-core systems should be improved. The improvement stems from the TCP and UDP sockets supporting a SO_REUSEPORT socket option that allows multiple sockets on the same host to bind to the same port.

Power consumption

The kernel will also support a "lightweight suspend" mode that is reported to allow some phones and tablets to consume almost as little power as when they are put into the deeper and less responsive suspend-to-RAM state.

The inclusion of Intel's PowerClamp driver will also allow the maximum power consumption of Intel processors to be throttled to limit a system's power consumption.

Raid support

The B-tree file system (Btrfs) has new Redundant Array of Inexpensive Disc (RAID) support, including experimental native support for RAID 5, block-level striping with distributed parity, and RAID 6, block-level striping with double distributed parity, in addition to Raid 0 and Raid 1 support. Embedding RAID capabilities within the file system should also make it simpler to manage the RAID array and restore data in the event of a failure.


Integrated into the 3.9 kernel are drivers for VMware's Virtual Machine Communication Interface (VMCI), which reduces the overhead in communication between virtual machines and their host.

The KVM hypervisor in the kernel will support the virtualisation features of the processors based on Arm's Cortex A15 core, allowing KVM to work on Arm cores.

Drivers for the Xen hypervisor in the kernel will also allow hotplugging of processors and memory components, allowing them to be swapped while the host system is running. The kernel's code for Microsoft's Hyper-V hypervisor also now supports the improved interrupt model introduced with Windows 8.

Graphics drivers

Support for AMD's forthcoming Fusion APUs based on its Richland architecture has been added. New AMD graphics chips are also supported, with the kernel's Radeon graphic driver now supporting the Oland graphics chips used on Radeon HD 8500 and 8600 cards. 

The graphics driver for the integrated GPU in Intel's upcoming Haswell processors has been tweaked to allow the graphics core to use less power when a single display pipe is used in the Embedded DisplayPort. Texas Instruments OMAP processor graphic drivers will also offer improved power management features and support OMAP5.

The Nouveau driver for Nvidia cards adds experimental automatic and manual fan controls for the NV40 and NV50 GPUs used on the GeForce series 6xxx to 9xxx cards. The kernel also now offers Nvidia Tegra 4 support. 

Changes to the locking mechanism used by graphics drivers should help prevent displays from temporarily freezing when the system checks available monitors.

Meanwhile updated code for compressing and decompressing LZO should allow for faster processing by CPUs.


The kernel includes a driver for Intel's series 7000 wi-fi components. The Ethernet subsystem features a driver for the AX88179 component used in a variety of USB 3.0 gigabit LAN hardware. Support for the Multiple Registration Protocol that was specified in IEEE 802.1Q-2011 has also been added to the network stack.

The driver code used to configure HD audio codecs is reported to have been made leaner and more robust. Support for Creative's CA0132 sound chip used in various motherboards has also been added.

Meanwhile the perf performance analysis tool now includes a test routine for measuring the memory performance of Non-Uniform Memory Access systems, with the kernel developers also shrinking some of the tracing data structures to improve performance.

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