“There are hundreds of these calls in the kernel.”
Linux papered over long-running kernel loops with hundreds of cond_resched() calls, each one a guess by whoever wrote that loop. Peter Zijlstra’s PREEMPT_LAZY aims to replace both PREEMPT_NONE and PREEMPT_VOLUNTARY, and Thomas Gleixner expects “less than 5%” of those calls to survive. Mike Galbraith’s early tests put throughput just short of PREEMPT_VOLUNTARY. Decades of sprinkled heuristics, and the fix is to delete most of them.