The release cycle of the Linux 6.19 kernel has faced some turbulence due to issues related to the NEXT_BUDDY scheduler feature. Initially enabled for EEVDF during the 6.19 merge window, the feature was meant to optimize scheduler performance. However, reports soon surfaced indicating performance regressions across various workloads such as MySQL, SPECjbb, DayTrader, and notably Nginx HTTPS server.
As a response to these performance issues, the Linux kernel development team decided to disable the NEXT_BUDDY feature in the release candidate 7 (rc7) stage of the 6.19 development cycle. This adjustment aimed to address the discrepancies observed during testing phases.
To understand the impact of this change, a series of fresh benchmarks were conducted, particularly on high-end hardware like the AMD Ryzen Threadripper PRO 9995WX. These benchmarks compared three configurations: the stable Linux 6.18 version, the Linux 6.19 Git version with NEXT_BUDDY activated, and Linux 6.19 with NEXT_BUDDY disabled.
The benchmark results underscored the significance of this decision, highlighting that disabling NEXT_BUDDY helped mitigate the performance regressions observed in the previously mentioned workloads. However, it is worth noting that disabling the feature might inadvertently affect workloads that initially benefited from it.
Until the root causes behind the performance drops are thoroughly understood and addressed, the NEXT_BUDDY feature will be maintained in a disabled state by default. Future kernel updates will likely revisit this feature in hopes of reintroducing it without the associated regressions.

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Linux 6.19 kernel disabled the NEXT_BUDDY scheduler feature in rc7 after it caused performance regressions in MySQL, SPECjbb, DayTrader, and Nginx HTTPS workloads. Benchmarks on AMD Ryzen Threadripper PRO 9995WX compared three configurations and confirmed that disabling NEXT_BUDDY mitigated the performance issues. The feature will remain disabled by default until the root causes are identified and resolved.

Analyzing the Impact of Disabling NEXT_BUDDY in Linux 6.19 Kernel Scheduler