Schedulers University of New Mexico - - PowerPoint PPT Presentation

Schedulers

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https://commons.wikimedia.org/wiki/ File:Simplified_Structure_of_the_Linux_Kern el.svg

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O(1) scheduler (older)

 Two arrays, switching between them is just changing a pointer  Uses heuristjcs to try to know which processes are interactjve

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Average sleep tjme

 htups://en.wikipedia.org/wiki/O(1)_scheduler

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CFS scheduler (currently in Linux)

 Completely Fair Scheduler  Red-black tree of executjon to the nanosecond

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niffjes

 Like weighted fair queuing for packet networks  An ideal processor would share equally  maximum executjon tjme = tjme the process has been waitjng to

run / total number of processes

 htups://en.wikipedia.org/wiki/Completely_Fair_Scheduler

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BFS (now MuQQS)

 Brain “Hug” Scheduler  Specifjcally for desktops  Weighted round-robin where the weights are based on some

very complex formulae (see Wikipedia for details)

 No priority modifjcatjon for sleep behavior  Time slice = 6ms (human perceptjon of jituer ≈ 7ms)  Performs slightly betuer than CFS for <16 cores  htups://en.wikipedia.org/wiki/Brain_Fuck_Scheduler  htups://lwn.net/Artjcles/720227/

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Windows NT through 10

• Multilevel Feedback Queue (MLFQ)

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Mac OS X

• XNU is a mix of FreeBSD and Mach

– Network, files, processes, POSIX interface,

• etc. come from FreeBSD

– CPU scheduling, memory management,

specialized IPC, etc. comes from Mach

• Round-robin and MLFQ schedulers

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IOS (i.e., iPhone)

• Same as Mac OS X

– MLFQ and round-robin

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Android

• Same as Linux

– Completely Fair Scheduler

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FreeBSD

• https://www.usenix.org/legacy/event/bsdco

n03/tech/full_papers/roberson/roberson.pdf

• ULE scheduler
• Looks a lot like Linux’s old O(1) scheduler

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Others

• GNU Hurd uses GNU Mach’s scheduler

– MLFQ and RR

• Haiku has a simple RR scheduler where the time

slice is based on the priority

• Solaris uses MLFQ
• Minix and xv6 - ???
• Real-time OSes - ???
• Supercomputers - ???