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SCHED_DEADLINE To Be Added To Linux 3.14 Kernel

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  • SCHED_DEADLINE To Be Added To Linux 3.14 Kernel

    Phoronix: SCHED_DEADLINE To Be Added To Linux 3.14 Kernel

    Less than 24 hours after the Linux 3.13 kernel release there's already interesting Git pull requests submitted for Linux 3.14...

    http://www.phoronix.com/vr.php?view=MTU3Njk

  • #2
    I don't really understand what this is good for... Desktop, Server, ... ?

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    • #3
      Originally posted by Article
      a real-time scheduling policy
      For real time workloads.

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      • #4
        Originally posted by droste View Post
        For real time workloads.
        Isn't SCHED_FIFO / SCHED_RR for this? Your answer doesn't help in any way. Again: Does this benefit desktop workloads (low latency) or servers or ... ?

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        • #5
          @TAXI:
          time constraints seems the key:
          http://retis.sssup.it/~jlelli/sched-deadline.php

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          • #6
            Originally posted by TAXI View Post
            Isn't SCHED_FIFO / SCHED_RR for this? Your answer doesn't help in any way. Again: Does this benefit desktop workloads (low latency) or servers or ... ?
            FIFO and RR are basic scheduling policies for realtime that considers resource allocation on a process by process basis. DEADLINE works on the entire list of tasks and is a pre-requirement for hard realtime. Real time schedulers are typically not used by either desktop or server since real time does not mean fast and they can reduce throughput considerably in some cases in order to provide the guarantees that comes as part of such scheduling. You might want to read through

            http://people.redhat.com/williams/realtime-training.odp

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            • #7
              Originally posted by RahulSundaram View Post
              FIFO and RR are basic scheduling policies for realtime that considers resource allocation on a process by process basis. DEADLINE works on the entire list of tasks and is a pre-requirement for hard realtime. Real time schedulers are typically not used by either desktop or server since real time does not mean fast and they can reduce throughput considerably in some cases in order to provide the guarantees that comes as part of such scheduling. You might want to read through

              http://people.redhat.com/williams/realtime-training.odp
              You use a realtime scheduler when Time, not performance or latency, is your most important performance metric. Embedded systems make a lot of use of real-time schedulers, for instance. When I want the task to, say, open/shut the fuel valve, I don't care about how the rest of the system performs; the task that needs to accomplish this task must be completed before "x" time, and ONLY a realtime scheduler can guarantee that will be the case.

              For normal Desktop/Server workloads, a realtime scheduler will cost you system performance.

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              • #8
                It is useful for embedded systems where meeting deadlines (determinism) is essential for real time processes (usually at the cost of less throughput)

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                • #9
                  Thanks for all the answers. But now I have to ask: I remember some discussions some time ago that realtime scheduling should be good for desktops, especially gaming. Was that just trolling?

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                  • #10
                    Originally posted by TAXI View Post
                    Thanks for all the answers. But now I have to ask: I remember some discussions some time ago that realtime scheduling should be good for desktops, especially gaming. Was that just trolling?
                    That's a soft realtime system versus a hard realtime.

                    The difference is that hard realtime provides guarantees, while soft just does it most of the time. I think a lot of people were talking about the soft rt patches working well on games by reducing input latency. I'm somewhat skeptical of using it for the entire desktop system, but it might be ok for most people.

                    No one is going to want the hard rt scheduling on games, i don't think. The benefit of hard rt is being able to deterministically prove things so you can always 100% guarantee the system works as expected - that's important when dealing with things that could be life threatening if they go wrong, or otherwise cause legal or financial issues.

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