Linux 6.15-rc1 Released with Major Driver Upgrades and Performance Gains

Linus Torvalds has announced the release of Linux kernel 6.15-rc1, marking the end of the merge window for this development cycle.

This first release candidate arrives two weeks after the stable Linux 6.14 kernel release, bringing significant updates across various subsystems.

A Larger Than Normal Merge Window

According to Torvald’s report, this release features a considerable amount of new code, making it “one of the bigger merge windows” due to accumulated development following previous release cycles affected by holiday seasons.

“It’s big in both number of commits and in lines changed,” Torvalds noted in his release announcement.

“While it’s bigger than normal, it’s not some kind of record-breaking thing: we’ve had bigger releases, although not many.”

The changes follow a typical distribution pattern with approximately two-thirds dedicated to driver updates, while the remainder covers architecture updates, filesystems, core kernel components (scheduling, timers, memory management, networking), and miscellaneous infrastructure improvements.

Key Technical Enhancements

The 6.15-rc1 kernel includes several notable technical improvements:

• Updated Zstd Compression: The in-tree Zstd compression code has been updated to version 1.5.7, bringing performance improvements
• Networking Enhancements: The io_uring An asynchronous I/O interface now supports zero-copy receive operations for network tasks, potentially delivering significant performance gains
• Filesystem Updates: Bcachefs has reached a “soft frozen” on-disk format state, indicating increasing stability for this filesystem
• Turbostat Expansion: Support for up to 8,192 cores in the Turbostat CPU monitoring utility (previously limited to 1,024 cores), driven by HPE’s needs for an unnamed 1,152-core system
• Performance Optimizations: Improved implementation of VAES-based AES-CTR encryption, resulting in significant speedup on CPUs like AMD Zen 5
• Boot Time Improvements: The new hugetlb_alloc_threads option helps optimize kernel boot time

New Hardware Support

Linux 6.15-rc1 enhances compatibility with various hardware platforms:

• Apple Silicon Support: New drivers for Apple M-series chips, including “apple_z2” for touchscreens and Touch Bar functionality, developed by the Asahi Linux project
• NVIDIA Support: Early-stage NOVA core driver for modern open-source NVIDIA kernel driver support, leveraging NVIDIA GPU System Processor (GSP) firmware for Turing and newer GPUs
• AMD Enhancements: AMD’s P-State driver received a major refactoring, eliminating redundant writes and optimizing lock management
• RISC-V Improvements: Better compilation system support and new instruction sets like BFloat16

Additional Features

Other noteworthy additions include:

• New setcpuid= boot parameter for x86 CPUs
• Support for sched_ext to count and report internal events
• Nested virtualization support for VGICv3 on ARM
• Updated ACPI fan and button drivers
• Intel TDX (Trust Domain Extensions) improvements for virtualization

Release Timeline

The final version of Linux kernel 6.15 is expected in late May or early June 2025, depending on how many release candidates are needed.

If the development follows a typical seven-RC cycle, we could see the stable release around May 25th; an eight-RC cycle would push it to approximately June 1st.

For developers and enthusiasts interested in testing this release candidate, it’s available from Linus Torvalds’ git tree or the kernel.org website, though it’s not recommended for production environments.

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