In anticipation of the forthcoming release of the stable Linux 6.14 kernel, a single patch has been merged into the mainline branch—reverting a two-year-old modification to the task scheduler. This rollback addresses a significant performance degradation observed under certain workloads.
Two years ago, a patch was introduced into the core logic of the kernel scheduler aimed at reducing the overhead of the sched_move_task function when the CONFIG_SCHED_AUTOGROUP option was enabled. Notably, in a simple test involving multiple invocations of the sleep command from a bash script, the change yielded a 57% performance improvement.
However, it was later discovered that this optimization adversely impacted other scenarios. An Amazon engineer, for instance, found that within the AWS environment, enabling autogrouping led to a performance drop of up to 30% in UnixBench’s spawn test. Other workload types were also negatively affected.
Ingo Molnar submitted a pull request containing this sole reversion and remarked, “This is admittedly a bit late in the cycle, and the regression is old, but the performance impact is substantial for the affected workloads so I didn’t want to delay this fix.”
Barring any objections from Linus Torvalds, the patch is expected to be incorporated into Linux 6.14 later.
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