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CPU Clocks and Clock Interrupts, and Their Effects on Schedulers

• ravanave 11y ago
  "A SPNT OS has no real need of a scheduler." I would rather disagree: https://en.wikipedia.org/wiki/Computer_multitasking https://en.wikipedia.org/wiki/Computer_multitasking. OS in the most of the cases needs to be interactive, what would be impossible without multitasking. Multitasking would not be possible without a scheduler. So, we would not swap the active task and we would be stuck with the current task forever (or until it finishes), without even the ability to interrupt it.
  • stefantalpalaru 11y ago
    > A single process, non-threaded (SPNT) OS runs one process at a time There's no multitasking in this scenario. Think MS-DOS 6.22.
    • ravanave 11y ago
      Of course, there does not have to be, but if there would then it would be very useful. Think MS-DOS 4.0 multitasking: https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking) https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking) One process can have a preemptive multitasking. Even one process can make a very good use of a scheduler.
• jdub 11y ago
  One interesting thing this (dated but still very relevant) article misses is timer coalescing. Most modern operating systems try to merge a bunch of timer actions into a single wake/interrupt. Not only does this leave more time for other work to be done in the normal case of a loaded CPU, but if there's less demand, it provides way more opportunity for the CPU to fall into a lower power state. Some timer APIs will let you specify how accurate you want your timer to be. Often enough, a few tens or hundreds of milliseconds doesn't really matter for your use case, but that's AEONS in CPU time!