Linux MMX removal targets the last Pentium-era RAID optimizations

Linux developers are preparing to remove the kernel’s last Intel MMX optimizations, closing a chapter that began with Pentium processors in 1997. The Linux MMX removal proposal targets specialized storage calculations while preserving existing software fallbacks. Its central tradeoff is straightforward: less legacy code for maintainers, with a possible performance cost for unusually old systems.

MMX, Intel’s instruction extension for processing packed data, once helped software accelerate multimedia and other repetitive calculations. The remaining kernel implementations serve software RAID, which combines drives under operating-system control. Those implementations now face retirement because generic alternatives already perform the same work.

The expected destination is Linux 7.5, anticipated in 2027, but that remains a release expectation rather than a completed mainline merge. For owners of affected hardware, the distinction matters. This proposal changes how particular storage calculations run; it does not itself establish that every Pentium-era computer can run a future kernel.

Linux MMX removal reaches beyond a single XOR routine

The proposal removes a small family of legacy RAID implementations, rather than disabling the storage feature they accelerate.

Eric Biggers submitted the series on October 25, 2026. Its MMX retirement proposal contains three patches covering XOR, RAID6, and processor feature checks. The submitted changes touch seven files, adding 12 lines and deleting 837.

XOR, a bitwise operation that combines values, helps calculate parity, the redundant information used to reconstruct missing data. RAID6, a storage arrangement designed to tolerate two drive failures, requires additional calculations beyond basic XOR. Treating the entire series as one deleted XOR routine therefore understates its scope.

The distinction also prevents an exaggerated reading of the headline. Removing an optimized implementation changes the available execution paths. Removing RAID support would eliminate a storage capability. The submitted proposal describes the former, with affected processors using existing generic code.

Phoronix reported that the work had reached Andrew Morton’s MM development tree and identified Linux 7.5 as the likely destination. Its kernel MMX coverage frames the release target as an expectation. As of November 9, that is the appropriate language for readers planning around the change.

A development tree provides evidence that work is progressing toward integration. It does not make a proposed release target unconditional. Review, integration decisions, and subsequent revisions can still affect what reaches a final kernel.

For readers encountering Linux MMX removal explained through nostalgic headlines, that status distinction deserves attention before the history. The verified event is a submitted cleanup series with a reported development-tree landing. The future event is its expected arrival in a mainline release.

The practical boundary is equally important. The series concerns implementations inside the kernel, the operating system’s core. It does not describe a general prohibition on applications using MMX instructions, nor does it announce that Intel processors will stop recognizing them.

That boundary changes the meaning of “end of an era.” The kernel would finish retiring its own MMX-specific optimization work. The broader software ecosystem, including historical applications and preserved operating systems, has a separate lifecycle.

For maintainers, the proposal presents a concrete opportunity to simplify a surviving corner of the code. For users, it raises a narrower question: whether their particular machine selects one of these implementations today. That question leads directly to the hardware requirements.

The affected systems sit below different instruction thresholds

The relevant dividing line is processor capability and workload, not simply whether a computer carries a Pentium badge.

Biggers’ XOR removal patch identifies the affected path as serving old 32-bit processors without SSE support. SSE, Streaming SIMD Extensions, is a later instruction extension for processing multiple data elements. The patch also limits the relevant usage to systems actually running a RAID array.

The RAID6 patch draws a different boundary: processors without SSE2, the subsequent extension in that instruction family. Its RAID6 implementation changes also remove a file named sse1.c. Biggers explains that this implementation still used MMX calculations, supplemented by SSE memory operations.

That filename is an instructive detail. A quick scan could suggest that the series removes an independent, modern replacement alongside MMX. The patch description instead identifies another implementation built around the older machinery.

For anyone evaluating Intel MMX performance impact, these separate thresholds matter. A processor’s support for SSE does not automatically settle its exposure to every part of the series. The selected implementation and the RAID calculation involved determine the relevant comparison.

Consider a hypothetical enthusiast running a supported kernel configuration on a preserved Pentium II storage machine. If its array uses a retiring implementation, the practical change would concern calculation performance. The presence of a fallback means the proposed code removal does not automatically eliminate that calculation.

Now consider a developer reading the same headline on a contemporary workstation. The age of the MMX instruction extension alone says little about that workstation’s selected storage implementation. The useful evidence would be its actual processor capabilities and kernel behavior.

These examples illustrate exposure rather than establish measured outcomes. The reviewed material does not provide an inventory of active machines using the retiring paths. It therefore cannot support a precise estimate of affected users.

The people facing a meaningful decision are operators who combine old processor capabilities with the relevant storage workload. They would need to establish whether an upgrade changes their selected implementation and whether any resulting slowdown matters.

Distribution maintainers face a related communication task. Their kernel configuration, package availability, and processor requirements remain separate from this optimization cleanup. Users need those details before interpreting a future release as an upgrade option for preserved hardware.

The maintenance tradeoff therefore reaches a narrow technical audience with potentially specific needs. Small exposure does not mean no exposure. It means the response should follow actual hardware and workload evidence, rather than the emotional weight of a familiar processor name.

Generic code keeps the capability while reducing special cases

The proposal separates preserving a function from preserving every historical implementation of that function.

A scalar fallback, ordinary code that processes values without the retired MMX implementation, gives maintainers that option. Biggers describes the existing fallbacks as well tested. That is the author’s stated basis for preserving functionality while removing specialized paths.

The phrase deserves its proper scope. It supports the proposal’s continuity argument, but it is not a published benchmark for every affected machine. Correct output and equivalent speed are different properties.

The maintenance logic is easier to understand when viewed as a choice between implementations. Specialized code can justify its presence when it serves users or delivers useful performance. Its continued existence also creates material that reviewers must understand when related code changes.

Generic code offers a shared place to maintain behavior. That does not make every specialized implementation unnecessary. It changes the evidence required to keep an old one: there should be a practical benefit worth preserving.

This is where Linux MMX removal becomes more interesting than a historical anniversary. The project is weighing a remaining performance path against the complexity of carrying it forward. The existence of a working alternative makes deletion possible without making the decision costless.

The third patch extends that simplification to processor feature checks, which select suitable implementations from available hardware capabilities. Biggers proposes removing redundant prerequisite checks and avoiding repeated checks for the same features. The submitted code retains newer implementations, including SSE2 and AVX2 paths.

AVX2, a later vector instruction extension, represents another route for processing multiple values in an operation. Its presence illustrates the technical comparison more clearly than a brand rivalry would. The issue is which implementation fits the processor and remains worth maintaining.

Intel’s name dominates the history because it introduced MMX. The actual maintenance decision is about supported processor features, rather than vendor branding. Comparing historical Intel and AMD products would not resolve whether a particular kernel implementation still earns its place.

The same reasoning explains why a line-count reduction needs careful interpretation. Fewer lines describe the size of a source change. They do not directly measure faster storage, fewer defects, or a specific reduction in maintenance hours.

The strongest case for the cleanup is therefore structural. A shared fallback preserves the calculation, while the series removes implementations intended for an older capability range. Performance claims require additional evidence.

Seen that way, Linux MMX removal explained is a story about narrowing the implementation burden around an existing capability. The kernel can keep doing a job while retiring one historical method of doing it. Whether that balance is right depends partly on the remaining users.

MMX’s long retirement reflects a changing maintenance bargain

The historical milestone is real, but MMX’s launch date does not measure the age or value of every deleted implementation.

Intel introduced the Pentium processor with MMX technology on January 8, 1997. Its contemporary Pentium MMX launch emphasized graphics, video, and audio. A technology marketed around richer personal-computer media eventually survived in kernel storage calculations.

That history explains why the proposal attracts attention beyond storage development. MMX was a visible consumer feature, associated with a recognizable period in personal computing. Its final kernel optimizations carry symbolic weight that ordinary cleanup work rarely receives.

The symbolism should not obscure the actual timeline. An instruction extension can predate code that uses it. Calling this the retirement of a 1997 technology is accurate; assuming every removed source line dates to 1997 would require separate evidence.

The proposal also follows earlier removals. Biggers points to a previous commit that eliminated MMX optimizations for memory functions, including memcpy(), copy_page(), and clear_page(). Those functions copy data or initialize memory, activities separate from the remaining RAID work.

Their earlier retirement changes the framing of the current event. This is the completion of a narrower cleanup sequence, rather than a sudden decision to expel a broadly used technology. RAID remained as an outlying kernel use after other optimization work had disappeared.

A historical optimization can lose its original rationale gradually. Hardware changes, alternative implementations arrive, and the population using the oldest path becomes harder to establish. The code can remain functional throughout that transition.

That creates a recurring maintenance question: how much ongoing attention should a project devote to a path whose practical audience is uncertain? Deletion is one answer when the capability survives elsewhere. Keeping the code is another when users demonstrate a meaningful benefit.

Neither position requires dismissing old hardware. Preservation work has different goals from maintaining a current general-purpose kernel. An enthusiast may value reproducing historical behavior even when that behavior no longer warrants a dedicated upstream implementation.

The reverse is also true. Nostalgia does not establish that specialized code has active users, current testing, or a useful performance advantage. Those are technical questions that deserve technical evidence.

The broader lesson is about the terms of compatibility. Keeping an algorithm available, retaining a processor-specific optimization, and supporting a complete machine are separate commitments. A project can alter one while leaving the others subject to their own requirements.

For developers, this is a useful example of how software ages without simply breaking. An optimization can move from essential to optional to difficult to justify. Its retirement then reflects a changed maintenance bargain, rather than a judgment on the hardware’s historical importance.

The missing evidence is measured performance on affected hardware

A preserved fallback establishes a route to continued operation, not a guarantee of unchanged performance.

The available patch descriptions explain why Biggers considers the specialized code obsolete. They do not provide a measured comparison of affected machines running representative storage workloads before and after the change. That leaves the practical cost unresolved.

This gap should limit claims in both directions. It would be premature to declare that every affected system will become noticeably slower. It would also be premature to promise that nobody will notice.

The Intel MMX performance impact depends on where time goes during a real operation. A slower calculation matters differently when processing is the limiting factor than when another component dominates. The proposal alone does not establish that balance for a specific machine.

An isolated calculation test would answer one useful question: how the old implementation compares with its replacement under controlled conditions. A storage workload would answer another: whether that difference changes the work an operator actually performs.

Those results should not be treated as interchangeable. A visible difference in calculation throughput does not automatically translate into an equivalent difference in application performance. Equally, an acceptable routine workload might overlook a less frequent operation that matters to its owner.

For a preserved storage system, maintenance activity could be as relevant as everyday access. An operator might care about recovery work, sustained writes, or processor availability during other tasks. These are proposed evaluation areas, not measured regressions established by the series.

The strongest objection would therefore come from reproducible results on an affected configuration. Such evidence could show that the specialized path retains practical value. It would give reviewers something more concrete than an assumption about how many old machines remain.

The strongest support would combine continued correctness with acceptable behavior on relevant hardware. That would strengthen the argument that the shared implementation meets remaining needs. Again, the proposal’s existence does not substitute for those observations.

Compatibility claims need similar restraint. Removing these optimization files does not establish a change to a stored array’s format. It also does not certify that every old system can boot a future kernel.

Users must evaluate the complete upgrade environment, including distribution requirements and their hardware configuration. A narrow source change cannot answer every question about a machine’s future support. Presenting it as such would confuse separate decisions.

There is also no basis here for advertising a broad security improvement. Reducing specialized code may simplify review, but the submitted rationale does not identify a vulnerability fixed by this deletion. Maintenance benefits should remain maintenance claims unless additional evidence supports more.

The responsible reading is consequently measured. The series offers a credible way to reduce legacy complexity while preserving calculations. The remaining debate concerns the value of the removed acceleration and the evidence needed to judge that value.

Watch integration, fallback testing, and distribution delivery

The next useful developments are observable milestones: mainline integration, testing on affected systems, and delivery through actual kernel packages.

First, watch whether the series reaches the mainline kernel and which release contains it. Linux 7.5 remains the reported expected destination. A confirmed merge would strengthen the release-specific story and provide a definitive change for downstream reviewers.

A revision, delay, or withdrawal would change that assessment. The broader proposal would still be documented, but the anticipated release timing would need updating. Readers should avoid converting a development-tree report into an unconditional release note.

The exact merged version will matter too. Review can alter scope or implementation details even when the overall direction survives. Following the accepted change provides a firmer basis for compatibility analysis than relying indefinitely on the initial submission.

Second, watch for correctness and performance results from hardware that actually uses the retiring paths. Tests on an unrelated newer processor cannot settle the experience of an affected legacy system. The relevant comparison needs a matching configuration and a clear workload.

A credible report should distinguish successful operation from satisfactory speed. It should also explain what was measured and whether the old implementation was selected before the change. Without that context, a result can be accurate yet irrelevant to the proposed tradeoff.

Acceptable results would reinforce the argument that generic code can meet the remaining need. A reproducible regression with operational consequences would weaken it. Either outcome would improve the discussion by replacing assumptions with evidence.

Third, watch distribution delivery. An upstream release does not establish when a user’s chosen distribution will package that kernel or support their machine. Package configuration and processor requirements remain part of the practical upgrade decision.

For someone maintaining an old system, the meaningful milestone is an available kernel that fits the complete environment. Until then, the proposal is relevant planning information rather than an immediate instruction to replace hardware.

These observations also keep the historical narrative proportionate. The retirement deserves attention because it closes a recognizable chapter in kernel optimization. Its technical importance will depend on what merges, how the remaining paths behave, and who encounters the change.

For engineering teams, keeping those distinctions documented can prevent a headline from becoming an unsupported compatibility assumption. A searchable knowledge base can connect the accepted patch, local configuration, and test results when evaluating upgrades.

If you maintain affected hardware, start with the configuration you actually run and the storage work you need it to perform. Record the selected implementation before testing a kernel containing the change. Compare results that reflect your workload, and separate correctness from speed. If you maintain newer systems, follow the accepted patch rather than treating every reference to MMX as a compatibility warning. Linux MMX removal will be most informative as a documented maintenance decision, with its benefits and costs tied to observable behavior. Follow the merge, examine relevant test reports, and check your distribution’s requirements before deciding what this retirement means for your machines.