June 4, 2018

Linux Kernel 4.17, "Merciless Moray," Offers Improved Performance and Security

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Linux kernel 4.17
Improved power consumption in Linux kernel 4.17 means battery charges will last longer on laptops, clusters will be more efficient, and machines will be more eco-friendly across the board.

Linus Torvalds released version 4.17 of the Linux Kernel on Sunday, nine weeks after the prior version. Although Linus says he is running out "of fingers and toes to keep track of minor releases," he has decided not to call this release "5.0" because he is saving that for 4.20.

As with the 4.16 cycle, 4.17 has been a relatively smooth, save a few hiccups due to those pesky chip issues. It turns out the shadow of the Spectre vulnerability is still long, and the last two weeks before the release were a busy ones, with patches designed to counteract the effects of Spectre v4 making up a significant portion of all the code submitted. That said, and even though Linus does not like large amounts of changes so late in the release cycle, he skipped an rc8 and released the final version of 4.17 anyway.

Be as it may, 4.17 also comes with plenty of other improvements. There is the set of changes that will improve the power consumption on most machines, for example. These changes affect what is called the "idle loop" of the kernel. Even if your machine is apparently not doing anything, as long as it is powered up, the kernel is working. The new code optimizes the "downtime" processes and, according to its author Rafael Wysocki, power consumption could go down "10% or more." This means battery charges will last longer on laptops, clusters will be more efficient, and machines will be more eco-friendly across the board.

Something that is not often mentioned in these reports are the various curios -- the leftovers from times gone by that still have developers working on them -- such as the case of the Macintosh PowerBook 100 series, a laptop series manufactured by Apple in the early 1990s which used a Motorola processor. These things are still being maintained, and 4.17 comes with several improvements for the devices. I wonder if it is too late to get the support for the Commodore 64 in there.

Although the PowerBook 100 is still being supported, on a more pragmatic note, other architectures have been dropped. Such is the case of eight obsolete CPUs, including the Unicore32, Blackfin, and Hexagon, among others. All of these processors are very niche and are being superseded by other more modern alternatives. Support for POWER4 and POWER4+ processors is also being removed. Considering IBM is now on the ninth generation of POWER, it was probably about time. Dropping these architectures has had the side effect of making 4.17 one of the lightest releases in recent years, where the number of lines removed is larger than the number of lines added. All told, getting rid of code for obsolete architectures eliminates about half a million lines from the kernel.

Other stuff to look forward to in kernel 4.17

  • Kernel 4.17 also comes with HDCP, or High-bandwidth Digital Content Protection. This is the technology that "protects" proprietary content by making perfectly functional, but uncertified hardware underperform or directly useless. This may seem counterintuitive, and it is. No buts. The idea is that, to protect music and videos, manufacturers must certify their video cards, monitors, and HDMI cables (and pay up considerable amounts of money) so that HDCP-protected content will play on the devices. If making software act as an obstacle on perfectly adequate hardware sounds like a bonkers idea, that's because it is. But that's the state of the protection of copyrighted material nowadays. At least in theory, the inclusion of HDCP is a step towards allowing user to be able to play protected content.

  • Fortunately, most code in this release improves performance on the users' machines. Changes in the realm of drivers/controllers and AMD video cards received a big boost this time around. In 4.17, AMDGPU DC is enabled by default, for example, and is now in the mainline kernel. This means you won't need to install an external DKMS driver for your Radeon card at full capacity, and you will have HDMI/DP audio out of the box. Another improvement is that AMDKFD is now also part of the mainline kernel. This is important for using AMD GPUs in high performance computing, where GPUs are used to carry out complex and consuming calculations.

  • Speaking of performance enhancements, work has begun on code that allows users to tweak the power management of their cards and the first changes have also been incorporated into 4.17: On other platforms, Radeon WattMan allows users to control the voltage, fan speed, engine clock and so on of their cards, and that is what developers are starting to work into the Linux kernel.

  • Support for the RISC-V, the open source processor architecture, is also chugging along nicely. Developers have added dynamic ftrace on RISC-V, cleaned up the atomic and locking routines, as well as the module loading support. The latter is now enabled by default.

As always, to find out more, you can check out Kernel Newbies (when it becomes available) and Phoronix.

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