While the ecosystem Linux continues to evolve, a new feature appears: lazy preemption, also called PREEMPT_LAZY. This innovative approach aims to optimize task management in the operating system. Through this article, we will explore the issues and advantages of this new option, as well as its potential impact on the general performance of the Kernel.
What is lazy preemption?
Definition and operation
Preemption is a key mechanism in an operating system, allowing a current task to be interrupted to give priority to another. With the implementation of PREEMPT_LAZY, a balance is sought between reactivity and performance. Concretely, this differential preemption model chooses not to systematically interrupt tasks SCHED_NORMAL, thereby reducing lock conflicts.
Operating principles
The approach is based on the use of an indicator, TIF_NEED_RESCHED_LAZY, which allows preemption to be deferred for certain classes of tasks. When lazy preemption is enabled, this is what happens:
- Tasks SCHED_NORMAL are less often preempted.
- Real-time tasks, such as RR, FIFO And DEADLINE, retain their maximum priority.
- Execution latency is reduced by minimizing expected interruptions.
Impact on performance
Comparison with other preemption modes
Lazy preemption is mainly designed to improve the classic preemption model. By revising the timing of interruptions, it seeks to reduce the performance gap with Volunteer by providing:
- Optimization in the processing of ordinary tasks.
- Increased flexibility for critical tasks.
- Visible performance gains in intensive applications.
Targeted architecture
Currently, PREEMPT_LAZY was mainly introduced for architectures x86, x86_64 And RISC-V. This orientation demonstrates a commitment to optimization on systems that frequently encounter bottlenecks due to competitive tasks.
Summary table of key elements
| 🔑Element | 💻Description |
| Lazy preemption | New task management model to reduce interruptions. |
| Class SCHED_NORMAL | Less often preempted for better lock management. |
| Real-time tasks | Remains a priority to guarantee maximum responsiveness. |
| Supported architectures | Currently x86, x86_64 and RISC-V. |
What do you think of this new introduction of lazy preemption? Share your opinions and thoughts in comments!