The official Linux 3.15 stable release won't come for about two months, but here's a look at the features we've been looking at for this next major kernel update:
- Many open-source kernel DRM driver improvements. The DRM pull includes much better support for upcoming Broadwell hardware, many other Intel i915 improvements, primary plane support, initial NVIDIA Maxwell support (but the Gallium3D Nouveau driver support isn't yet ready for NVIDIA's Kepler successor and 3.15 still depends upon the binary blob's microcode), the Radeon driver has its VCE 2.0 video encoding support, other Radeon DRM updates, and numerous other changes to the growing number of DRM graphics drivers.
- Partial support for LTO but the actual Link-Time Optimization Kconfig options to complete the experimental feature haven't yet been pulled by Linus Torvalds as he isn't sure about LTO support for the Linux kernel in its current state. Link-time optimizations should reduce binary sizes and provide faster binaries, among other benefits, but for now will cause longer build times and excessive use of system RAM.
- EFI Mixed Mode Support so that a 64-bit Linux kernel can boot even if the system UEFI is 32-bit. There's been some flaky hardware that's Intel x86_64 capable but shipping with 32-bit firmwares and now with UEFI mixed mode support this issue may be a matter of the past (though the very latest Intel devices seem to be better about 64-bit UEFI support).
- File-system work for Linux 3.15 included Btrfs performance fixes and addressing potential Btrfs corruption, F2FS large directory support, and various EXT4 and XFS file-system updates. There's also better write performance for FUSE-based file-systems.
- AVX-512 support for future Intel CPUs / Xeon Phi. There's also Intel RDSEED support for better hardware-based randomness.
- ACPI and power management updates that include faster suspend and resume times.
- Besides the ACPI/PM suspend and resume improvements, work by Intel for Linux 3.15 should lead to much faster resume times with being able to power-up disks and other SCSI devices in parallel without blocking the kernel until the devices are ready.
- Kernfs has grown to be more useful for other kernel subsystems, after its logic was split out of sysfs in Linux 3.14.
- Improved Windows guest support with KVM virtualization.
- Sony DualShock 4 controller support and other input device improvements.
- New notebook support.
- Many audio and sound improvements.
- Among the other pulls this cycle include AHCI libata updates, scheduler improvements, removal of some old x86 platform support, new media/V4L2 drivers, support for a new WiFi adapter, and ARM SoC updates.
Update: Another last-minute feature worth mentioning -- LLVM's Clang can almost compile the Linux kernel!