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By The Linux Camp News, October 26, 2026
A fix reported merged into Linux 7.4 Git addresses slow Clang full-LTO builds on Ryzen AI 9 HX 370. Cache locality will no longer block placement on a preferred idle core; stable backports remain to be verified.
On October 26, 2026, Phoronix reported that Linux 7.4 Git had received a scheduler fix for a cache-aware scheduling regression affecting at least AMD’s Ryzen AI 9 HX 370. Ingo Molnar’s scheduler pull request confirms the fix’s inclusion and purpose, but the merge-completion claim comes from Phoronix, not the pull request itself. 1 4
The reported symptom was a long build despite idle fast cores. Gentoo user Klaus Kusche described Clang full link-time optimization, or LTO, leaving one process running for minutes. Earlier kernels moved that work to a fast core; with cache-aware scheduling, work started on a little core stayed there. Tim Chen’s patch attributes the penalty to both lower frequency and half as much L3 cache. 2 3
Two placement policies conflicted. Asymmetric packing favors higher-priority CPUs, while cache-aware scheduling groups a process’s tasks within one last-level cache, or LLC, domain. On the reported machine, fast and little cores occupy separate L3 domains. Preserving cache locality therefore blocked the move to a faster core, even when every fast core was idle. 3 2
The fix changes precedence rather than removing cache-aware scheduling. When asymmetric packing seeks an idle, higher-priority destination, it can override the cache-placement preference. Chen’s patch applies that priority to both regular and active load balancing, allowing the scheduler to favor the faster available core over keeping work within its existing cache domain. 3
For affected build machines, check whether the running kernel’s package includes this fix, not merely whether a newer package is installed. As of source retrieval on October 26, Phoronix named 7.2 and 7.3 as backport targets, not shipped fixed releases. Backporting also means the base kernel version alone is insufficient: package-level patch inclusion is the relevant check. 1 3
The supplied patch carries three Tested-by tags, including Kusche’s, but supplies no quantitative build-time recovery. The demonstrated workload is HX 370 full-LTO linking. Phoronix suggests other mixed-core Ryzen processors might benefit; that remains a possibility, not broad hardware validation. 3 1