Preemption of CFS scheduling

Conclusion analysis

1. No way policy Can be preempted , such as sched_normal policy You can seize sched_idle policy The task of . sched_batch Don't take
2. Wake up task and fantasy task when waking up , If two features next_buddy as well as last_buddy If it is opened , It can support preemption
3. If wakeup Mission vruntime Time is less than curr Of vruntime Time , The difference is greater than sysctl_sched_wakeup_granularity, Is set next_buddy (set_next_buddy)

# Functions involved
check_preempt_wakeup May be set NEXT_BUDDY and LAST_BUDDY, cfs_rq There are next and last The pointer , Support preemption
place_entity （ The sleep process and the newly created process will be allocated vruntime Time slice ）
pick_next_entity

Main function analysis