linux-upstream

Why this build?

Ubuntu 24.04 ships kernel 6.8. This build is Linux 6.19 with two targeted scheduler fixes for Intel hybrid P/E core processors:

• Fork placement fix — new processes had a 50/50 chance of starting on slow E-cores even when fast P-cores were idle. Fix adds ITMT priority comparison in update_pick_idlest(), improving P-core placement from 50% to 100%
• Wake-affine fix — once a task landed on an E-core, it would return there forever due to cache-warmth preference overriding core priority. Fix adds ITMT priority scanning in select_idle_sibling() and wake_affine_idle(), improving P-core wakeup from 0% to 98%
• Zero overhead on non-hybrid CPUs — on AMD, older Intel, or ARM processors the fix compares zero values and takes no extra cycles
• 9-test validation suite — includes an ITMT simulation kernel module and comprehensive scheduler edge-case tests (fork placement, idle wakeup, RT preference, affinity constraints, producer-consumer, short-lived tasks, yield stability, overload balancing, wake-affine chains)