软实时/硬实时需求里，主线内核默认抢占往往不够。PREEMPT_RT 把自旋锁等路径改成可抢占，降低最坏延迟，但要配合隔离核、关机外干扰与实测。
源码锚点
| 路径 / 手册 | 作用 |
|---|---|
Documentation/scheduler/ |
调度说明 |
kernel/sched/ |
调度实现 |
tools/rt-tests/ |
cyclictest 等 |
man chrt |
设调度策略 |
调用链
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中断
唤醒实时线程
调度器选中 SCHED_FIFO/DEADLINE
用户态循环
延迟直方图
重点知识
延迟从哪来
中断下半部、关抢占临界区、同核干扰、电源管理休眠、SMI（x86）、显卡锁。RT 内核降低部分最坏情况，不能替代 dual-OS/AMP 硬实时方案。
观测
bash
cyclictest -p 90 -i 1000 -l 100000
chrt -f 90 ./my_rt_app
# isolcpus / cpuset 隔离实践要点
- 实时线程绑核，避开 IRQ 重载核。
- 避免在 RT 线程里写磁盘、打日志刷屏。
- 先测空载基线，再加业务。