lecture9

thread

 

 

 

 

 

lecture10

I/O层

 

 

 

 

 

 调度

1.最小化响应时间

2.最大化吞吐量

3.分配时间公平

 FCFS

后面的短请求，要等待前面的长请求。 

Round Robin Scheduling

Each process gets a small unit of CPU time (time quantum), usually 10-100 milliseconds – After quantum expires, the process is preempted and added to the end of the ready queue. – n processes in ready queue and time quantum is q  » Each process gets 1/n of the CPU time » In chunks of at most q time units » No process waits more than (n-1)q time units

 

调度公平

如果job6得到锁，job1开始，就会发生优先级反转，解决方法是如果job1放弃调度的话，放回job6(持有锁的那个)