6.15

Featured

Ranked in smallest to biggest (all X86):

Cleanup in the Cryptography code yielded up to 23% boost for AES-XTS. This patch work by correcting the possibility of the IRQ (interrupts) to fail and fallback on unoptimized code. [10]

AES-CTR optimized using AESNI+AVX+VAES giving us insane result up to 240% check →[15]

CRC (Error detection checksums) big optimization after using x86 optimization (AVX-512) on them,

from 4x to 29x depending on use cases!!!![12]

IO_uring network zero-copy(doesn't have to go through the CPU to transfer) receive support.

This means that a 200G link could be saturated on a single core which was unthinkable before.

The big fix is that the kernel can directly put the data into the application memory instead of having to get the it in kernel mem and copy it in app mem [34]

FineIBT exploits. Can be enabled if compile with LLVM and with boot option "cfi=fineibt+bhi". No docs on how to BHI part of the mitigation works yet...[3]

BENCHMARK From Phoronix:

Bcachefs, Btrfs, EXT4, F2FS XFS File-System Performance On Linux 6.15 - Phoronix

The TLDR is that BcacheFS is getting demolished in almost every category (but has some wins...).

Even is BcacheFS is performing worst than EXT4 in a lot of Bench, we need to keep in mind that it isn't competing with it, it is competing with ZFS. ZFS also get beaten by EXT4 in a lot of metric.

The true winner here is XFS, it trounced its competition to the point where there is no reason why you should use anything else if you are performance minded.

FS

Block device now supports Block size bigger than page size. The support for it in VFS and XFS was already implement in 6.12 but is also needed to be implemented at the block device level.[31]

BcacheFS

XFS

BTRFS

FUSE

EROFS

-EXT4

System V FS was removed from the kernel as it was unused and unusable.[32]

Also fun fact, it was converted to the "New" mounting API before it was remove.[42]

-DM changes[33]

CPU

AMD

add feature INVLPGB with some very nice perf bump (2X) Linux Kernel Patches To Use AMD INVLPGB Instruction Show Huge Speed-Up - Phoronix[1]

continued work on the AMD node driver after 6.14 decoupling

-Zen 5 Load Latency Filtering[14]

Intel

Continued work over CPU identification that started in 6.12. Moving forward Intel CPUs will appear in Family 19 like Diamond Rapids. The kernel will now use new VMF macros for encoding the Vendor, Family, Model information instead of relying on the Model id.[2]

-continued work on Linear Address Masking (LAM)

Allow mitigation to only be applied to E or P cores (instead of all cores), Intel's motivation for this is initially around the Register File Data Sampling (RFDS) vulnerability where only the E cores on Alder Lake and Raptor Lake are susceptible to the issue.[4]

Initial work on tech in future CPU; Advanced Performance Extensions (APX) [11]

TDX.[20]

x86

New "setcpuid=" boot parameter for overriding the exposed CPU features. Part of an effort for running mitigations on CPUs that don't need them, good for kernel devs! [5]

Large ROX (Read-Only eXecutable) pages can now be used to load kernel modules. was attempted on 6.13 but needed final cleanup.[6]

all part of a big cleanup for 32 bit code that lives with 64 bit code:

End of support for KVM 32bits host (guest still compatible)[8]

End of support for over 4 GB of memory on 32Bits (Called HIGHMEM64G or PAE)[9]

-Kernel address space layout randomization (KASLR) entropy is being reduced on most x86 systems now in order to support PCI BAR space beyond the 10 TiB region.[7]

RISC-V

Support for a lot of new extensions[16]:

BF16

Zicbom

Zaamo

Zalrsc

Zicntr

Zihpm

LoongArch

bunch of small features including[17]:

Fixed and improved BPF JIT

Fixed and improved vDSO

MIPS

Even if MIPS won't be getting any future CPU (MIPS Technologies Joined RISC-V) the Linux code is still getting updates for the last EyeQ6 along with all other MIPS.[21]

GPU

Initial skeleton for Nvidia Rust-Based driver Nova[23]

Intel Xe Driver introduced Shared Virtual Memory allowing is to use ram from the system shared by the CPU [24]

Intel Xe Driver introduced Protected Xe Path (PXP HWDRM), will be used for DRM content to stay encrypted until it is in the GPUs memory where it can be drawn on screen.[26]

AMD and Intel added a standardized way to notify User-space when a GPU becomes unresponsive. This could allow User-space processes to attempt recovery.[25]

AMDGPU Supports OEM I2C bus used for RGB lightning control or displays, we don't have controls for now but this is a first step into having customizable RGB like on windows.[29]

-Intel Xe EU Stall Sampling Support[24]

-Intel Xe3 upcoming GPUs, new feature "allowing frame-buffer compression (FBC) on dirty rectangles" [27]

-Intel now allows GuC SLPC power profile to be tuned[28]

Network

Linux now has support for MCTP over USB (Management Component Transport Protocol).

MCTP is a protocol for communication through a system, it support pretty much everything Management Component Transport Protocol - Wikipedia.[35]

Security

mseal() can now be used for system mappings such as the vDSO. It is disable by default as it will probably break a bunch of stuff[40] [43]

Memory Management

New boot option can control how many thread will be used for Huge Pages initialization. this can yield boost in boot speed when tweaking correctly. New default is 25% of available thread which seems to give the best bang for you buck (follow link for image)[41]

Huge Pages allocator now more reliable, allocation of huge pages is a big issue on Meta's servers and being more and more essential for their workload, work on fragmentation is always welcome as it will yield more successful huge pages allocations.[41]

Misc

New Minimum:

GCC: 8.1

LLVM: 15.0

Python: 3.9

NEW SUBSYSTEM FWCTL Seeks to standardize the way drivers and hardware expose a secure firmware interface to user space. Pioneered by Nvidia, also used for CXL and AMD.[36]

Turbostat now supports 8192 CPU cores instead of 1024, HPE(HP-Enterprise) reported that they breached the limit with a 1152 core system.... [13]

Regression (up to 50% loss of perf) in CPUIdle Governor on Tickless Systems has been fixed[18]

-KVM update i skiped [19]

Hardware

Support for Apple T2 security co-processor, which is another computer on your compute, This is needed for a bunch of features on that mac that have it...[22]

Support for Apple Z2 (Protocol for) touchscreen/touchbar driver[37]

Support for Apple Touch Bar on older Intel x86 Macs and a newer "ADP" driver for handling the Apple Touch Bar displays on the newer Apple M1/M2-powered MacBooks.[30]

Someone back in 6.13 started working on compatibility for older iPad, iPhone and iPod Touch devices, we now have a backlight driver for those devices38] [cursed

Support for MNT Reform 2 Laptop which is very ugly but is open source and modular... [22]

Cleanup and update of the General Purpose Interface Bus (GPIB) which is a 50YO connector that is still used for some scientific equipment.[39]

Linus' RC messages

Linux 6.15-rc1 - Linus Torvalds

Linux 6.15-rc2 - Linus Torvalds

Linux 6.15-rc3 - Linus Torvalds

Linux 6.15-rc4 - Linus Torvalds

Linux 6.15-rc5 - Linus Torvalds

Linux 6.15-rc6 - Linus Torvalds <----- Contains a fun fact that Linus gave up on trying a quieter keyboard

Linux 6.15-rc7 - Linus Torvalds

Linux 6.15 - Linus Torvalds

Sources:

  1. : AMD INVLPGB Merged For Linux 6.15 To Provide Another Performance Advantage - Phoronix

  2. : Intel Wrapping Up Family 18 / Family 19 CPU Model Preparations Ahead Of Linux 6.15 - Phoronix

  3. : Linux FineIBT-BHI Updated For Toughening Up FineIBT Kernel Defenses - Phoronix

  4. : Linux 6.15 Set To Include Better Handling For Intel P Or E Core Only Mitigations - Phoronix

  5. : Linux 6.15 Goes Very Heavy On Intel AMD x86_64 CPU Changes - Phoronix

  6. : Linux 6.15 Looks Like It May Try Again With EXECMEM_ROX Support - Phoronix

  7. : Linux 6.15 Goes Very Heavy On Intel AMD x86_64 CPU Changes - Phoronix

  8. : New Linux Patches Cleanup Code For Running x86 32-bit Kernels On x86_64 CPUs - Phoronix

  9. : x86 32-bit Changes Look To Be Ready For Linux 6.15 - Drops Support For More Than 4GB RAM - Phoronix

  10. : New Patches Would Make All Kernel Encryption/Decryption Faster On x86/x86_64 Hardware - Phoronix

  11. : Faster Intel/AMD Crypto Performance Initial Intel APX Enablement Slated For Linux 6.15 - Phoronix

  12. : Linux 6.15 CRC Code Should See Big Speed-Ups For Intel/AMD AVX-512 CPUs - Phoronix

  13. : Turbostat Utility Bumps 1024 CPU Core Limit To 8192 Cores After HPE Breaches It With 1152 Cores-Phoronix

  14. : Linux 6.15 Performance Events Adds Support For AMD Zen 5 Load Latency Filtering - Phoronix

  15. : Linux 6.15 Crypto Subsystem Delivers Faster AES-CTR For AMD Zen 5 Other x86_64 CPUs - Phoronix

  16. : RISC-V With Linux 6.15 Adds Support For BFloat16 "BF16" Instructions - Phoronix

  17. : LoongArch Enables A Few More Features With Linux 6.15 - Phoronix

  18. : Linux 6.15 Further Improves AMD P-State Driver, Intel Dev Tackles A ~50% SPEC Regression - Phoronix

  19. : Many KVM Updates Merged For Linux 6.15 - Phoronix

  20. : Intel TDX Is Becoming Potentially Faster, Avoiding "Slow Buggy" Code Path On Linux - Phoronix

  21. : MIPS Lands Multi-Cluster Support In Linux 6.15 For The EyeQ6 SoC - Phoronix

  22. : Linux 6.15 SoC/DT Additions: Arm Morello, Versal NET, Apple T2, MNT Reform 2 More - Phoronix

  23. : The New Rust-Written NVIDIA "NOVA" Driver Submitted Ahead Of Linux 6.15 - Phoronix

  24. : Intel Xe Driver Introducing SVM, EU Stall Sampling Other New Features For Linux 6.15 - Phoronix

  25. : Linux Finally Introducing A Standardized Way Of Informing User-Space Over Hung GPUs - Phoronix

  26. : Linux 6.15 Intel Xe Driver Enabling PXP HWDRM, Survivability Mode GPU + VRAM Temperatures-Phoronix

  27. : Intel Preps Xe3's "Dirty Rect" Feature For Linux 6.15 - Phoronix

  28. : Intel Graphics Driver With Linux 6.15 To Allow Tuning The GuC Power Profile - Phoronix

  29. : AMD Linux GPU Driver Preps OEM i2c Bus Support Used For RGB Control More - Phoronix

  30. : Apple Touch Bar Display Drivers Slated For Introduction In Linux 6.15 - Phoronix

  31. : Code Submitted Ahead Of Linux 6.15 For Enabling Block Sizes Greater Than Page Size - Phoronix

  32. : SystemV Filesystem Being Removed From The Linux Kernel - Phoronix

  33. : Linux 6.15 Device Mapper Brings Inline Crypto Passthrough For DM-Stripe - Phoronix

  34. : IO_uring Network Zero-Copy Receive Lands In Linux 6.15 - Phoronix

  35. : MCTP-Over-USB Driver Slated For Linux 6.15 - Phoronix

  36. : New FWCTL Subsystem Submitted For Linux 6.15 - Phoronix

  37. : Apple Z2 Touchscreen / Touch Bar Driver Lands In Linux 6.15 - Phoronix

  38. : Linux 6.15 Landing Backlight Driver For Various Apple iPhones iPads - Phoronix

  39. : Linux 6.15 Brings Improvements For Five Decade Old GPIB Bus - Phoronix

  40. : MSEAL Protection Of System Mappings Merged For Linux 6.15 - Phoronix

  41. : Linux 6.15's New "hugetlb_alloc_threads" Option Can Help Speed-Up Boot Times - Phoronix

  42. : The first part of the 6.15 merge window [LWN.net]

  43. : The rest of the 6.15 merge window [LWN.net]