Re: Task priorities in non strictly real-time systems

From	Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: Task priorities in non strictly real-time systems
Date	2020-01-06 19:47 +0200
Organization	Tidorum Ltd
Message-ID	<h7ha4pFrjcnU1@mid.individual.net> (permalink)
References	(1 earlier) <qunihq$450$1@dont-email.me> <quradg$h90$1@dont-email.me> <qutd6p$om0$3@dont-email.me> <quttqq$vhf$1@dont-email.me> <h7h7fdFr0f8U1@mid.dfncis.de>

Show all headers | View raw

On 2020-01-06 19:01, Hans-Bernhard Bröker wrote:
> Am 06.01.2020 um 01:08 schrieb Don Y:
> 
>> Preemptive frameworks can be implemented in a variety of ways.
>> It need NOT mean that the processor can be pulled out from under
>> your feet at any "random" time.
> 
> I think I have to disagree with that.
> 
> Let's start with linguistics.  To "preempt" means: to get in ahead of
> someone (or something) else.
> 
> In the RT world, that something is a running task, and preemption
> happens when some other task gets to use the CPU before that task is
> done with it.  I.e. a preemptive framework, pretty much by definition of
> the words, does pull the CPU out from under you, and that _will_ happen
> at, essentially, random times.
> 
> If the running task can routinely (as opposed to exceptionally) avoid
> that happening to itself, that means it's essentially the other type of
> framework: a cooperative one.

There are lots of intermediate ideas, "limited preemption" systems. See 
"Limited Preemptive Scheduling for Real-Time Systems: a Survey", at
https://algo.ing.unimo.it/people/marko/papers/TII13.pdf

> Now we in c.a.embedded don't usually get to make that distinction quite
> so cleanly of course, because for us, ISRs are a fact of life, and those
> are always preemptive.

Except, of course, when the task that would be interrupted disables or 
masks the interrupt(s) for a while, thus delaying the 
interruption/preemption until later.

Some embedded programs run with all interrupts always disabled, and 
instead poll for inputs and events.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .

Thread

Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-03 14:41 +0100
  Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-03 15:19 +0100
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:25 +0100
      Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:32 -0600
        Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-05 16:49 -0500
          Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:05 -0600
        Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-05 17:08 -0700
          Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:26 -0600
            Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-05 22:10 -0700
              Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-06 07:37 -0600
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 17:21 -0700
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 19:23 -0600
              Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-06 20:36 -0500
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 01:38 -0600
                Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 06:53 -0500
            Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 07:13 -0500
            Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-07 10:11 +0100
              Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 07:05 -0500
              Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 19:34 -0600
          Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-06 10:44 +0200
            Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 02:51 -0700
              Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-06 15:39 +0200
                Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 13:29 -0500
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 14:38 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 07:05 +0200
                Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-07 13:09 -0500
                Re: Task priorities in non strictly real-time systems Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-07 20:53 +0200
                Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-08 08:43 +1100
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-08 00:33 +0200
                Re: Task priorities in non strictly real-time systems Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-08 15:26 +0200
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-08 00:08 +0200
                Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-07 10:37 +0100
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 16:10 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 07:37 +0200
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 01:49 -0600
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:43 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 10:21 +0200
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:42 -0700
                Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 22:23 -0500
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-09 22:07 +0200
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 10:54 +0200
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:43 -0700
          Re: Task priorities in non strictly real-time systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-06 18:01 +0100
            Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-06 19:47 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:58 +0100
      Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-05 14:26 +1100
        Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-05 11:21 +0200
          Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 14:07 +0100
            Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-05 17:46 +0200
              Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 19:08 +0100
        Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 13:56 +0100
        Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:39 -0600
          Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-06 07:44 +1100
            Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:00 -0600
              Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-06 14:50 +1100
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-06 07:12 -0600
      Re: Task priorities in non strictly real-time systems Paul Rubin <no.email@nospam.invalid> - 2020-01-04 22:34 -0800
        Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 14:12 +0100
          Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-05 18:00 +0200
        Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:44 -0600
      Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 14:52 -0500
      Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 15:05 -0500
        Re: Task priorities in non strictly real-time systems gtwrek@sonic.net (gtwrek) - 2020-01-06 22:41 +0000
        Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 19:50 -0700
          Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-07 13:26 -0500
  Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-03 16:28 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:37 +0100
      Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:46 -0600
        Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-05 22:44 +0200
  Re: Task priorities in non strictly real-time systems Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-03 11:49 -0800
  Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-03 22:51 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:48 +0100
  Re: Task priorities in non strictly real-time systems Joe Chisolm <jchisolm6@earthlink.net> - 2020-01-03 15:34 -0600
  Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-03 21:46 -0500

csiph-web