December 13, 2016

Linux Kernel 4.9 Is Here, and It's the Largest Release Ever

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Roaring Lionus
Linus Torvalds released Linux kernel 4.9 -- aka Roaring Lionus. Here is a breakdown of some of the many changes.

Linus Torvalds released Linux kernel 4.9 on Sunday and christened it "Roaring Lionus" in honour of the anonymous barista that flubbed his name on his morning cup of coffee.

With regard to volume, this is probably the largest kernel release ever. There have been more than 16,000 non-merge changesets into the mainline repository over this two-month merge window. This number is well over the 13,722 changesets for 3.15, which held the record up until now.

The most active group of developers have been the team formed by Johan Hovold, Viresh Kumar, Greg Kroah-Hartman, and Alex Elder, who are working on the Greybus code. The most active employer by number of changesets was Linaro with 1,876 changesets, mostly related to, again, Greybus.

Interestingly, the Raspberry Pi Foundation makes the list of the 20 most active employers by lines of code for the first time, with 12,816 lines contributed. However, that number is still far behind the two leaders, AMD and Red Hat, each of which contributed more than 100,000 lines.

The details

What the heck is this Greybus that is stirring up such a raucousness? You may have heard of Project Ara, a Google-backed phone project that would let users build their own device using a variety of modular hardware blocks. Given a basic frame, a user could add on a camera or two, a wide range of sensors, or screens with different resolutions, loudspeakers, and so forth, using a set of Lego-like blocks.

Unipro is the protocol developed back in the day by Nokia and Phillips that would allow the modules interconnect with each other on a hardware level... and Greybus is the software driver layer that gives the Linux kernel support for Unipro-based modules. Although Google pulled the plug on project Ara back in September, the idea of modules does live on in other phones, such as the Moto Z series and the LG G5. If the concept of modular phones catches on, the effort put into Greybus will not have been in vain.

In other news, as Linus remarks in his post, two thirds of the bulk of changes are drivers. Apart from the Greybus drivers, there is also the usual slew of new drivers and patched drivers for GPUs. AMD came in first as the employer with most lines contributed -- for their Southern Islands cards -- to Mesa's DRM library, and drivers for the Vulkan API continue to improve and support more software and hardware.

Another set of drivers that is getting improvements is Intel's Skylake family of processors. Sound on many newer HPs, Dells, and Lenovos is now a lot less buggy, and the same goes for Intel's GPUs.

Also new in 4.9

The number of ARM machines supported by the mainline kernel continues to grow. New additions are the Raspberry Pi Zero, the BeagleBoard-x15 rev B1, and LG's Nexus 5 phone. That means no more customized compiling for these devices.

Kernel 4.9 also comes with improved BBR congestion control algorithms. LWN says these bits of code "allow network protocols (usually TCP) to maximize the throughput of any given connection while simultaneously sharing the available bandwidth equitably with other users." That means that your shared network speed is going up. When we're talking network connectivity, faster is always better, right?

Finally, there are improvements for several commonly used file systems, such as Btrfs, XFS, F2FS, and EXT4 across the board. These changes improve their performance and reliability. If you're looking for even more details, Michael Larabel at Phoronix has an extensive breakdown of all that's new in 4.9.

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