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Re: From cooperative to preemptive scheduler [Stack]

From Hans-Bernhard Bröker <HBBroeker@t-online.de>
Newsgroups comp.arch.embedded
Subject Re: From cooperative to preemptive scheduler [Stack]
Date 2020-01-15 21:51 +0100
Message-ID <h89caeFskkmU1@mid.dfncis.de> (permalink)
References <qv0lmu$up1$1@dont-email.me> <qvkc2v$3p8$1@dont-email.me> <h86i1qFaiccU1@mid.dfncis.de> <qvmitp$c8o$1@dont-email.me>

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Am 15.01.2020 um 09:36 schrieb pozz:
> Il 14/01/2020 20:10, Hans-Bernhard Bröker ha scritto:
>> Am 14.01.2020 um 13:27 schrieb pozz:
>>> Another trouble I found with a preemptive RTOS is how to size the stack
>>> of tasks.
>>
>> That trouble is not at all particular to preemptive scheduling.
>>
>>> In my superloop cooperative scheduler:
>>
>>> the stack is assigned to all the unused memory available in the system
>>> (that is all the memory minus variables and heap size, if you use it).
>>
>> And how do you know that that's sufficient?
> 
> I'm not too smart to estimate the stack usage of a function (I know the
> compiler can produce some useful info about this, but you should add
> interrupt stack usage and so on), so my approach is only tests.

As the saying goes: testing proves diddly-squat.  You'll hardly ever
know whether your test cases came anywhere near exercising the code path
of worst stack usage.

>> The difficulty of (reliably) computing stack usage is the same,
>> regardless what tasking concept is used.
> 
> I don't agree.

You disagree to a different statement than the one I made.  I was
talking about this job being difficult. You object based on it being a
lot to work.

> Most of the time I can guess what is the task (or a few tasks) that
> consumes more stack. 

Guessing is about the only approach to this that is even less reliable
than testing.

> In preemptive scheduler, you would need to multiplicate your effort to
> estimate stack usage for every single task to avoid wasting precious
> memory.

The effort doesn't really multiply, because it'll all be handled by
loops in the code anyway.  Doing the same thing multiple times is what
CPUs are supposed to be good at, after all.

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From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-07 02:08 +0100
  Re: From cooperative to preemptive scheduler: a real example Don Y <blockedofcourse@foo.invalid> - 2020-01-06 19:37 -0700
    Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-07 10:11 +0100
      Re: From cooperative to preemptive scheduler: a real example Don Y <blockedofcourse@foo.invalid> - 2020-01-07 07:51 -0700
        Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-07 23:51 +0100
          Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-09 01:39 +0200
            Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-10 00:42 +0100
              Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-15 18:39 +0200
          Re: From cooperative to preemptive scheduler: a real example Don Y <blockedofcourse@foo.invalid> - 2020-01-08 23:12 -0700
            Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-10 00:49 +0100
          Re: From cooperative to preemptive scheduler: a real example Don Y <blockedofcourse@foo.invalid> - 2020-01-08 23:12 -0700
          Re: From cooperative to preemptive scheduler: a real example Don Y <blockedofcourse@foo.invalid> - 2020-01-09 01:33 -0700
  Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-07 09:38 +0200
    Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-08 00:02 +0100
      Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-09 00:54 +0200
        Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-09 12:19 +0100
          Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-09 14:03 +0200
            Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-10 00:32 +0100
              Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-15 18:53 +0200
                Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-16 14:48 +0100
                Re: From cooperative to preemptive scheduler: a real example upsidedown@downunder.com - 2020-01-16 21:04 +0200
                Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-16 22:24 +0200
                Re: From cooperative to preemptive scheduler: a real example pozz <pozzugno@gmail.com> - 2020-01-17 02:05 +0100
                Re: From cooperative to preemptive scheduler: a real example Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-18 23:03 +0200
  Re: From cooperative to preemptive scheduler [Stack] pozz <pozzugno@gmail.com> - 2020-01-14 13:27 +0100
    Re: From cooperative to preemptive scheduler [Stack] Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-14 20:10 +0100
      Re: From cooperative to preemptive scheduler [Stack] pozz <pozzugno@gmail.com> - 2020-01-15 09:36 +0100
        Re: From cooperative to preemptive scheduler [Stack] Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-01-15 11:30 +0100
          Re: From cooperative to preemptive scheduler [Stack] pozz <pozzugno@gmail.com> - 2020-01-15 11:51 +0100
        Re: From cooperative to preemptive scheduler [Stack] Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-15 21:51 +0100
    Re: From cooperative to preemptive scheduler [Stack] Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-15 21:26 +0200
      Re: From cooperative to preemptive scheduler [Stack] Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-15 22:12 +0100
        Re: From cooperative to preemptive scheduler [Stack] Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-15 23:30 +0200

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