CODEWITHSUNDEEP
scheduler
Mustafa
Mustafa

Reputation: 101

Completely Fair Scheduler vs Round Robin

In the text books they say that the major advantage of CFS is that it is very fair in allocating CPU to different processes. However, I am unable to know how CFS with the RB-Tree is capable of achieving better form of fairness than that achieved by simple Round Robin queue ! If we forget about CFS grouping and other features, which can also be incorporated somehow in simple RR queue, can anybody tell me how CFS is more fair than RR? Thanks in advance

Upvotes: 3

Views: 4214

Answers (1)

fstonedahl
fstonedahl

Reputation: 127

I believe the key difference relates to the concept of "sleeper fairness".

With RR, each of the processes on the ready queue gets an equal share of CPU time, but what about the processes that are blocked/waiting for I/O? They may sit on the I/O queue for a long time, but they don't get any built-up credit for that once they get back into the ready queue.

With CFS, processes DO get credit for that waiting time, and will get more CPU time once they are no longer blocked. That helps reward more interactive processes (which tend to use more I/O) and promotes system responsiveness.

Here is a good detailed article about CFS, which mentions "sleeper fairness": https://developer.ibm.com/tutorials/l-completely-fair-scheduler/

Upvotes: 6

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