The first release candidate (RC1) for the Linux kernel version 6.15 is now available. This release marks the end of the merge window and presents a significant amount of new code and updates across various kernel subsystems.
In the Kernel 6.15-rc1 release announcement mail, Linus Torvalds noted that this release is not record-breaking in size, attributing its larger footprint to accumulated development following holiday periods.
As expected, this was one of the bigger merge windows, almost
certainly just because we had some pent-up development due to the
previous releases being impacted by the holiday season.That said, while it's bigger than normal, it's not some kind of
record-breaking thing: we've had bigger releases, although not many.
The really big releases tend to be due to some long-running major
development being finally merged after many years, and this is not
that: this is just the "regular" kind of big.
Table of Contents
Overall Scope of Changes
The 6.15-rc1 release incorporates a high number of commits and changes to the codebase.
Developers have contributed updates across a wide spectrum of the kernel. Notably, approximately two-thirds of the changes involve driver updates for different hardware components.
The remaining updates include a mix of architecture-specific improvements, filesystem enhancements, core kernel modifications (such as scheduling, timers, memory management, and networking), and miscellaneous infrastructure updates.
These infrastructure changes encompass areas like devicetree bindings, further integration of Rust, and an update to the Zstandard (Zstd) compression algorithm.
Linux Kernel 6.15 Key Highlights and Feature Improvements
The notable key features and improvements included in the Linux kernel 6.15 are given below.
Networking Enhancements
The io_uring asynchronous I/O interface now supports zero-copy receive operations for network tasks.
This enhancement can lead to significant performance improvements for network-intensive applications by reducing data copying overhead.
Filesystem Updates
The Bcachefs filesystem has reached a stage where its on-disk format is considered "soft frozen". This designation implies that future format updates will be optional, indicating increasing stability for this filesystem.
The in-tree Zstd compression code has been updated to version 1.5.7, bringing performance improvements and other enhancements.
Furthermore, various filesystems have received specific updates from their maintainers, including XFS, Btrfs, ext2/udf/isofs, ext4, NTFS3, Bcachefs, EROFS, and exfat.
Graphics Driver Developments
A significant addition is the early-stage NOVA core driver. This driver serves as a foundational element for a modern open-source NVIDIA kernel driver.
It will leverage the NVIDIA GPU System Processor (GSP) firmware to support Turing and newer NVIDIA GPUs.
Additionally, the kernel includes new driver support for AMD graphics hardware.
Apple hardware support is improved with the inclusion of the Apple Z2 touchscreen/touchbar driver and the Apple Touch Bar DRM display driver code.
Processor and Architecture Specific Optimisations
Support for the AMD Versal NET System-on-Chip (SoC) has been added.
Newer AMD processors benefit from the merging of AMD INVLPGB, which allows for an optimisation in broadcast Translation Lookaside Buffer (TLB) invalidation.
Cryptographic performance sees improvements with faster AES-CTR performance on AMD Zen 5 and various other Intel and AMD CPUs.
The release also includes numerous architecture-specific updates for ARM64, LoongArch, m68k, powerpc, RISC-V, sh, s390, and x86.
Core Kernel and Boot Improvements
A new boot option, hugetlb_alloc_threads, can potentially speed up kernel boot times. The kernel now includes necessary changes to support block sizes larger than the kernel page size, which is an underlying architectural improvement.
Tools and Debugging Capabilities
The perf performance analysis tool gains new latency profiling capabilities. Updates to the kernel debugger (kgdb) and perf tools are also present.
New Subsystem: FWCTL
A new subsystem called FWCTL has been merged into the kernel. As mentioned in Kernel documentation, fwctl's purpose is to define a common set of limited rules that allow user space to securely construct and execute RPCs inside device FW.
Continued Driver Development
As is typical for Linux kernel releases, a substantial effort has gone into updating and adding device drivers across a wide range of hardware categories.
These updates span various interfaces and device types, including I3C, RTC, GPIO, PCI, USB, sound, networking, storage, and many others.
Rust Integration
The ongoing effort to integrate the Rust programming language within the kernel continues with the inclusion of more Rust infrastructure.
Try Linux Kernel 6.15 RC1
The users and developers are encouraged to try the new Linux Kernel 6.15 RC1 and report back if there are any issues.
Linux Kernel 6.15 RC1 can be downloaded from the Kernel.org website or the Linus Torvalds's git tree.
Estimated Kernel 6.15 Final Release Date
Linux follows a time-based development cycle, which usually runs for about seven to eight weeks from the -rc1 release to the final release.
The Kernel 6.15 RC1 is tagged on April 6, 2025 (Sunday). Each week after that, a new release candidate (-rc2, -rc3, etc.) is published on Sundays.
Typically, Linus Torvalds releases the final kernel after rc7 or rc8, depending on stability and how many regressions or issues arise.
If the Linux 6.15 cycle follows the usual 7-rc pattern, we can expect the final release on May 25, 2025. If it requires 8 RCs, then June 1, 2025 is more likely.
Keep in mind that this is an estimate based on the typical release cycle, and the actual release date could vary slightly.
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