With the usual two weeks difference with respect to the previous stable, the publication of the can versiondidata Linux 6.15-rc1 has arrived Marked by a combination of technical innovations and strong public criticism from Linus Torvalds of a flawed implementation within the kernel tree. This initial development phase of version 6.15 reflects not only the size and diversity of its integration window, but also the attention to detail required to avoid errors that profoundly affect both developers and end users.
With a high load of changes that had accumulated due to interruptions for previous holidays, This release features major updates to drivers, architecture subsystems, compression, performance, and new device support.But its release has also been overshadowed by a glitch in the "hdrtest" test controller, which has outraged Torvalds himself.
Linus Torvalds attacks "hdrtest" and demands its immediate removal
One of the most talked about points of this cycle has been the inclusion of a code snippet known as “hdrtest”, designed for the DRM graphics rendering subsystem, specifically focusing on support for the Intel Xe driver. This code is intended to verify headers during the compilation process, but its implementation has generated unwanted temporary files that litter the kernel tree.
Torvalds expressed his anger at discovering that this tool was not an activatable option., but it was executed automatically, introducing slowdowns in the compilation process and generating “turd” files that interfere with basic functionalities such as autocompletion of commands in Git“This has to die,” was his emphatic statement on the matter.
The problem was detected because those files were not ignored in Git, which caused warnings in the repository status.Torvalds believes the failure lies not in the existence of the tool, but in the way it was integrated without allowing its optional use.
General updates in Linux 6.15-rc1: performance improvements and new hardware
The core remains focused on Improve performance, especially on recent AMD and Intel architecturesOne of the most notable changes in this regard comes from the cryptographic subsystem, which now offers an improved implementation of VAES-based AES-CTR encryption, resulting in a significant speedup on CPUs like AMD Zen 5.
Furthermore,Optimizations have been introduced to improve kernel boot time, thanks to the new “hugetlb_alloc_threads” option and improvements to compression systems like Zstd, updated in this version to align with version 1.5.7.
AMD's P-State driver has received a major refactoring, eliminating redundant writes and optimizing lock management. Regression issues in games due to conflicts with address space randomization (KASLR) have also been fixed, a solution contributed by an NVIDIA engineer who, ironically, was the original person responsible for introducing the bug.
Linux 6.15-rc1 also improves compatibility with Apple devices and RISC-V architecture.
Version 6.15-rc1 brings with it Support for touchscreens and the Touch Bar on Apple devices with M-series chips, thanks to the new “apple_z2” driver, developed by the Asahi Linux project. This change is significant for those looking to run Linux on recent Apple hardware without losing key features.
In parallel, the RISC-V architecture has also received attention., with improvements to its compilation system, support for new instructions such as BFloat16, and optimizations that improve the use of translated memory through the TLB.
Beyond the Core: Enhancements to Build and System Analysis Tools
Another area with multiple changes has been the Kbuild construction infrastructure., which introduces performance improvements to tools like “gendwarfksyms.” This utility, intended to facilitate the integration of the Rust language into the kernel, is now over 50% faster at resolving fully qualified names of exported symbols.
Also Support for architectures such as LoongArch has been added to distributions such as Debian. Improvements have been implemented for build reproducibility by allowing relative paths in source files and improvements to RPM package management with new debugging information.
In parallel, The kernel's performance analysis capabilities have been expandedAMD has introduced a new feature to filter load latency events on Zen 5 processors, allowing events to be analyzed only when a certain latency threshold is exceeded. Intel, for its part, has enabled PEBS counter snapshotting for more accurate sampling of performance events.
Patch to improve TDX and mitigate performance issues in virtual loads
In the field of virtualization, Intel has improved support for TDX (Trust Domain Extensions), with a fix that prevents the use of the HLT instruction inside protected virtual machines. This instruction caused slow virtualization exceptions and system behavior errors. Thanks to this fix, a considerable improvement has been observed in benchmarks such as SPECjbb2015, although concrete figures have not yet been published.
The solution was implemented by using existing paravirtualized infrastructure that allows HLT to be replaced with more efficient methods.. Additionally, an alert system has been introduced to detect if this instruction accidentally sneaks into future builds.
Linux 6.15-rc1 demonstrates that Although the core continues to grow in functionality and hardware support, poorly managed integration issues can trigger strong responses from its founder.. Improvements range from new drivers to architecture-specific performance tweaks, while maintaining a constant watch on code quality that enters the main repository.