Abstract
- Also known as Quantums
- The period of time for which a Process (进程) is allowed to run in a Preemptive Scheduling system
Attention
The length of each time slice can be critical to balancing system performance and process responsiveness - if the time slice is too short then the Process Scheduler will consume too much processing time, but if the time slice is too long, processes will take longer to respond to input.
Thus, we have Minimum Granularity to control the resource usage of process scheduler and Target Latency to ensure the responsiveness of the system.
Minimum Granularity
- Minimum Granularity is the minimum time period the Time Slice should have, this guarantees a minimum amount of CPU time for each process gets before being preempted
Control resource usage of process scheduler
Process preemption is an expensive operation, it involves Context Switch and change in Privilege Level. Thus, minimum granularity ensures the resource cost of process scheduler is controlled.
Info
In Linux Kernel, the minimum granularity is
0.75ms.
Target Latency
- The maximum amount of time that a Process (进程) should wait before being given a chance to run again
Ensure the responsiveness of the system
The target latency configured is not noticeable to users, so the process doesn’t seem laggy on the user side.
Info
Target latency will exceed when we have too many process and we need to ensure Minimum Granularity. That is why our computers are laggy when we are running too many programs and why a rebooting helps to speed up the computer.
Info
In Linux Kernel, the minimum granularity is
6ms.