Linux 6.5 Delays x86 FPU Initialization As Part Of Cleaning Up The Kernel Boot Process

The in-development Linux 6.5 kernel is shifting to initializing the x86 floating-point unit (FPU) initialization later in the boot process as part of a broader effort for trying to clean-up the Linux kernel boot process at least on x86/x86_64 systems.

Thomas Gleixner of Linutronix, which is owned by Intel since early 2022, has been leading his team to work on cleaning up the Linux x86 boot process. A main focus of that has been on cleaning up "the complete horror show of CPUID evaluation, which is constructed with hay-wire circuits, duct tape and superglue."

As part of that they've been working to move the initialization of infrastructure that isn't required during the early boot phase to happen later on. Gleixner commented on the patch series at the time, "Early boot is fragile and convoluted enough already, so anything which can move into a later phase is a win. X86 FPU initialization is one of the obvious parts which has zero justification to be done early."

That change to defer the x86 floating point unit initialization until later in the kernel boot process has now been merged as part of Linux 6.5. This late x86 FPU initialization makes up the x86/boot pull request that's now been merged to mainline for making the Linux x86 boot process a little less fragile while the broader Linux boot clean-up work is still ongoing.