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Re: Task priorities in non strictly real-time systems

From Don Y <blockedofcourse@foo.invalid>
Newsgroups comp.arch.embedded
Subject Re: Task priorities in non strictly real-time systems
Date 2020-01-07 06:42 -0700
Organization A noiseless patient Spider
Message-ID <qv21sf$1ip$1@dont-email.me> (permalink)
References (5 earlier) <lip51ftl0i2d7k01kcooh72hvs8ie4f5bd@4ax.com> <quuvup$pu6$1@dont-email.me> <eo861fle1ub0mbtbf1dtf1nntn5uldqqbg@4ax.com> <qv0eon$ttb$1@dont-email.me> <pmf81fp4fatrii64uutootcjrul7pq2dvk@4ax.com>

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On 1/7/2020 1:21 AM, upsidedown@downunder.com wrote:
> On Mon, 6 Jan 2020 16:10:03 -0700, Don Y <blockedofcourse@foo.invalid>
> wrote:
> 
>>> In a typical RT system nearly all (and most of the time all) task are
>>> in some sort of wait state waiting for a hardware (or software)
>>
>> Misconception.  That depends on the system's utilization factor
>> which, in turn, depends on the pairing of hardware resources to application
>> needs.
> 
> In my experience, keep the long time average CPU load below 40-60 %
> and the RT system behaves quite nicely.

The devices I've designed typically operate at, near or *BEYOND* 100%.
Time spent doing nothing means you've got resources that you don't need.
Resources = product cost.  (most of my past work was done pinching
pennies; the idea of *adding* hardware to a design was anathema!)

[I can recall recoding FINISHED code to replace 3-byte instructions
with 2-byte instructions; or eliding an opcode by rearranging the
order of register assignments; or noticing if the CY was set so
I could eliminate an increment following an add by replacing it with
an add-with carry.... all to see if I could trim a few hundred bytes
out of the running/tested binary to remove a ROM device from the
bill of materials!]

If you design systems to gracefully degrade and recognize that almost
all RT problems are "soft" -- or can be made so -- and know how to design
in that arena, then there's no real downside to designing for no margin.

The system with the barcode reader that I described elsewhere frequently
ran into overload.  Things would get "sluggish", occasionally.  But, never
broke.  (The barcode reader would typically tie up much of the machine's
"real time" for a tenth of a second)

The barcode reader, itself, became sort of a game; folks would rub
labels back and forth across the detector as fast as they could
in an attempt to crash the device.  You'd watch the display start
to get sluggish.  UARTS would stop transmitting.  Keypresses
would take longer to be recognized.  etc.

But, it wouldn't take long before "arms got tired" and the system
rebounded.  (lots of colorful/obscene comments when you'd watch someone
doing this sort of thing!  :> )

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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

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