Kernel 5.2-rc1 is Released with A Lot of Changes and Potential Performance Improvements

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Kernel 5.2 is shaping up to be a really big big release compared to 5.0 and 5.1. The amount of changes in this version is unusually high. On the graphics side there's now support for Intel Icelake and Elkhart Lake graphics, AMDGPU FreeSync improvements, support for the GeForce GTK 1650 in Nouveau and fixes for Valve's Index VR headset. And that's just scratching the surface.

A torrent of new CPUs are supposed. This includes Intel's Comet Lake CPUs and Agilex SOCs, ARM boards like NanoPi Neo2 and Jetson Nano and new AMD EPYC CPUs.

FPU state handling Finally re-worked

For performance there's x86 FPU state handling changes[1] which should give a measurable improvement. This is a pretty big fundamental change.

"I love this and we should have done it long ago, but I also worry that every time we've messed with the FP state, we've had interesting bugs. Which is obviously why we didn't do this long ago."

Faster memory allocations

A series of patches to vmalloc.c which tracks of free memory blocks should give large speedups to memory allocation operations[2]. This is a pretty big change to a critical area so the potential for bugs is there. The advantage of having a map of free memory which can be instantly used instead of having to look for free memory areas when you need them is clear. It would be nice if this works as expected and it makes into the final 5.2 release.

File-system improvements

On the file-system side of things EXT4 now supports per-directory case-insensitive files and folders. This may sound like a step backwards but it is really useful when running Windows software in WINE or Steam's Proton. Both btrf[3] and xfs[4] and even good old jfs[5] have gotten many updates.

Better support for Peripherals

Users of Logitech products can look forward to actual hardware-specific features on mouse and keyboards from that brand. Those products have so far been seen as Generic Human Interface Devices. Kernel 5.2 brings driver support specific to Logitech devices. This makes it possible to read battery state and finally use those extra keys on Logitech Coreless Desktop Pro" keyboards from 2002.[6] It only took 17 years to get Linux support for that fancy Internet Explorer button on those keyboards.

KVM virtio OpenGl still broken

There's KVM related changes and fixes[7] but one is, as of today's git, not fiex: Starting QEMU with -vga virtio -display gtk,gl=on on machines with AMD GPUs makes the Linux virtual machine hang when the host is using Linux Kernel 5.1 or newer. 5.2rc1 still has this problem. The 5.0.X series does not.

New mitigations= option to disable workarounds for Intel CPU bugs

A new option for disabling code which works around CPU bugs called mitigations= was introduced in 5.2. This option has been back-ported to all the "stable" series of earlier kernels and you are probably able to use this option if you updated your kernel the last few weeks - even if your distribution is using an older "stable" series like 4.9.x or 4.14.x


Kernel 5.2rc-1 can, as always, be download from kernel.org. You are probably better served doing

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

if you want to try the technology of the future today as it is easier to just git pull than download and extract when the next release candidate is announced.

Links and Notes


published 2019-05-23last edited 2019-06-17


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