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The long road to lazy preemption in the Linux CPU scheduler
[LWN subscriber-only content] Some review Current kernels have four different modes that regulate when one task can be preempted in favor of another. PREEMPT_NONE, the simplest mode, only allows preemption to happen when the running task has exhausted its time slice.
But a higher level of preemption can hurt the overall throughput of the system; workloads with a lot of long-running, CPU-intensive tasks tend to benefit from being disturbed as little as possible. There is also, of course, the need for extensive performance testing; Mike Galbraith has made an early start on that work, showing that throughput with lazy preemption falls just short of that with PREEMPT_VOLUNTARY. It all adds up to a lot to be done still, but the end result of the lazy-preemption work should be a kernel that is a bit smaller and simpler while delivering predictable latencies without the need to sprinkle scheduler-related calls throughout the code.
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