Linux 7.5 to Remove Final Intel MMX Optimizations from Software RAID

Linux developers are preparing to remove the last remaining Intel MMX optimizations from the kernel. A patch expected to merge into mainline Linux 7.5 will remove MMX-optimized code from software RAID XOR code, Phoronix reports. The kernel release is expected in 2027.

What the patch changes

Admittedly, there was not much left in Linux in terms of MMX optimizations. The change will remove MMX-optimized code from software RAID XOR code, so a determined late-1990s Pentium devotee can still use software RAID, but it will lack the MMX fast path. With this change, the kernel will lose over 800 lines of code and replace them with just 12. This is described as a classic case of Linux code housekeeping.

MMX in Linux history

Few folks will be running the most modern kernels on Pentium MMX and Pentium II chips in 2026. Most other MMX-optimized code disappeared from the OS half a decade ago, when some MMX-optimized memory management code was removed. The removal means Intel's ancient MultiMedia eXtensions become an irrelevance in the open-source OS.

Remembering MMX

Intel first introduced MMX Pentium chips in January 1997. Though the processors were marketed as being enhanced by MultiMedia eXtensions, Wikipedia insists that MMX is officially a meaningless initialism trademarked by Intel. In a subsequent trademark battle with longtime foe AMD, a document produced in court indicated that MMX stood for Matrix Math Extensions. AMD relied on this to sidestep the trademark, as an initialism cannot be trademarked, according to the encyclopedic source. Eventually, all rival x86 processors managed to integrate MMX instructions. Along with Pentium MMX chips, AMD, Centaur, Cyrix, Rise, and Transmeta eventually offered MMX CPUs. After MMX's marketing success, AMD pioneered 3DNow! instructions, and about a year later, Intel fired back with SSE and SSE2.

Sources: Tom's Hardware