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File systems

Ext4 will now by default use the "Multiple Page-IO Submissions" mblk_io_submit option, which is said to considerably improve performance and scalability. The code behind it was already added to the kernel with version 2.6.37, however, was disabled by default before the final because it caused data corruption in certain situations. Still labelled as experimental, the Btrfs file system will, from 2.6.39, offer Batched Discard functionality that were – introduced with 2.6.37, this feature uses the fstrim command line program to occasionally inform SSDs about unused storage areas.

The new Pstore file system gives access to "platform-persistent storage" – non-volatile, and usually small, storage areas that some systems provide so that operating systems can store information that is useful to diagnose the cause of a system crash. LWN.net provides background information about this in the article "Persistent storage for a kernel's 'dying breath'".

Storage

Jens Axboe has done considerable internal restructuring work in the block subsystem. The changes delegate some of the tasks involved in writing from a device-specific buffer closer to the code that needs to write the data (see 1, 2). The measure is designed to improve scalability, and therefore the kernel's performance with the fastest storage media that is currently available. This "new block device plugging model" was the only change Linus Torvalds specifically pointed out in his release email for the first release candidate of 2.6.39; Torvalds said that the approach avoids locks in busy code paths, cleans up the code and "should generally be a really good idea".

The kernel hackers have extended the LIO (Linux-Iscsi.org) target implementation they integrated with 2.6.38 to include the tcm_loop module; this module makes local SPC-4 SCSI emulations possible with arbitrary raw devices. The drivers ahci and ata_piix now support Intel's "Panther Point" chipsets (see 1, 2) in the 2.6.39 kernel. Intel is expected to introduce these chipsets together with new processors in early 2012. The .39 kernel's AHCI driver can address Marvell's 88se9125 PCIe SATA 6G controller (see 1, 2). The SCSI subsystem now offers improved support for the Logical Block Provisioning interfaces defined in the T10 specification for SBC3r26. It can inform SSDs and network storage solutions with Thin Provisioning about newly available memory areas via the SCSI commands WRITE SAME and its UNMAP-Bit (see 1, 2).

Downloading the Linux kernel

New versions of Linux can be obtained from the Kernel.org servers; the contents of these servers are also mirrored on numerous mirrors internationally. However, Linux users who are not familiar with the details of the kernel and its environment should generally not install new Linux drivers and kernels themselves but use the kernels provided by their Linux distributors instead.

Drivers

The USB code now supports USB 3.0 hubs (see 1, 2). The audio subsystem now includes a driver for the Terratec DMX 6Fire USB; a FireWire audio driver that addresses the Griffin FireWave surround sound system and LaCie FireWire speakers has also been added. Also new is a driver for the Technisat USB 2.0 DVB-S/S2 receiver. Another addition is the nw80x gspca subdriver that addresses webcam chips by Divio.

A driver for SABI has managed to leave the staging area. SABI is a Samsung interface that allows many of the netbooks and notebooks released by the manufacturer in recent years to inform the operating system of user events such as the pressing of function keys – for example the keys that regulate display brightness or sound volume.The .39 kernel also includes a driver for recent ASUS notebooks that use WMI to tell the operating system about function key events; this driver was created from the WMI driver for Eee PCs.

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