Scheduling in Linux and Windows 2000.pptVIP

Scheduling in Linux and Windows 2000 CS 431 Sanjay Kumar (01D07041) Sanjay Kumar Ram (01D07042) Linux kernel Linux process Scheduling policy Data Structures and Scheduling Algorithm in Uniprocessor System Scheduling algorithm for multiprocessor Scheduling in windows 2000 Linux Kernel Linux Processes Three class of processes Interactive processes Batch processes Real-time processes Linux processes have the following states: Running Waiting Stopped Zombie Scheduling Policy Linux kernel is non-preemptive but processes are preemptive The set of rules used to determine when and how selecting a new process to run is called scheduling policy Linux scheduling is based on the time-sharing technique -several processes are allowed to run concurrently“ CPU time is roughly divided into slices“ scheduling policy is also based on ranking processes according to their priority Static priority - assigned by the users to real-time processes and ranges from 1 to 99, and is never changed by the scheduler Dynamic priority - the sum of the base time quantum (the base priority of the process) and of the number of ticks of CPU time left to the process before its quantum expires in the current epoch Scheduling Policy (contd.) Process Preemption When the dynamic priority of the currently running process is lower than the process waiting in the runqueue A process may also be preempted when its time quantum expires How Long Must a Quantum Last? Quantum duration too short - system overhead caused by task switching becomes excessively high Quantum duration too long - processes no longer appear to be executed concurrently, degrades the response time of interactive applications, and degrades the responsiveness of the system The rule of thumb adopted by Linux is: choose a duration as long as possible, while keeping good system response time Data Structures and Scheduling Algorithm in Uniprocessor System The Linux scheduling algorithm works by dividing the CPU time into epoch