Re: Why does the location of PAD move around?

From	Alex <alex@rivadpm.com>
Newsgroups	comp.lang.forth
Subject	Re: Why does the location of PAD move around?
Date	2017-04-10 09:29 +0100
Organization	A noiseless patient Spider
Message-ID	<ocffk0$ah6$1@dont-email.me> (permalink)
References	(7 earlier) <oc74ge$13r3$1@gioia.aioe.org> <oc7g1i$laa$1@dont-email.me> <oc9amm$1oja$1@gioia.aioe.org> <ocai59$ldc$1@dont-email.me> <ocejqb$1clq$1@gioia.aioe.org>

Show all headers | View raw

On 4/10/2017 01:31, HAA wrote:
> Alex wrote:
>> On 4/8/2017 01:25, HAA wrote:
>>> Alex wrote:
>>>> On 4/7/2017 05:26, HAA wrote:
>>>>> Paul Rubin wrote:
>>>>>> "HAA" <someone@microsoft.com> writes:
>>>>> ...
>>>>> IMO the mechanism used by Forth Inc (and consequently L&P) to
>>>>> switch tasks is more complicated than it needs to be.  Executing
>>>>> instructions in user variables, splitting PAUSE into two fragments,
>>>>> seems a lot of effort when all that's needed is a tight loop that tests
>>>>> a flag e.g.
>>>>>
>>>>>        begin
>>>>>           mov  bx, [bx+cell]    \ point to STATUS of next task
>>>>>           cmp  [bx], 0             \ is task active?
>>>>>        0<> until
>>>>>
>>>>> The original method is cute - but justified?
>>>>>
>>>>>
>>>>>
>>>>
>>>> This burns CPU, which might be OK in a standalone environment; but even
>>>> there, it is incredibly wasteful of power. Polling will not work
>>>> satisfactorily in many hosted environments; for example, running on an
>>>> operating system like Linux or Windows.
>>>
>>> A round-robin with no active tasks, or a Linux/Windows with no event to drive
>>> them, means burning CPU.  You're only option in that case is to wind down
>>> power consumption.
>>>
>>
>> That's not how Linux or Windows works or any half decent scheduler of my
>> experience. As long as the processor has (1) a HALT or equivalent
>> instruction and (2) can resume from the halt in response to external
>> interrupts, there is no need to spin on the spot.* In Windows this is
>> managed by the system idle task. The OS should always be asked to wait
>> on an event on your behalf.
>>
>> *There are some spin locks required in multi processor systems, but
>> we're now way off the reservation.
> 
> Let's get back to your complaint above that my task switching code 'burns
> CPU'.  Well so does every Forth round-robin tasker I've seen.  If you believe
> my code represents a backward step, please explain in what way.
> 

Any technique that requires burning CPU while doing nothing is no more 
than a historical curiosity. Anton's recent interesting summary of 
Philae's activities didn't include a paragraph about mission failure 
because a spin wait on the RTX Forth chips depleted the batteries on the 
trip from earth to asteroid.

See my other reply to Elizabeth for the Windows case.

-- 
Alex

Thread

Why does the location of PAD move around? Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-01 21:07 -0400
  Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-01 19:32 -0700
    Re: Why does the location of PAD move around? Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-02 02:00 -0400
      Re: Why does the location of PAD move around? Julian Fondren <julian.fondren@gmail.com> - 2017-04-01 23:51 -0700
        Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-01 21:59 -1000
        Re: Why does the location of PAD move around? krishna.myneni@ccreweb.org - 2017-04-09 09:54 -0700
  Re: Why does the location of PAD move around? Julian Fondren <julian.fondren@gmail.com> - 2017-04-01 20:10 -0700
    Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-01 18:39 -1000
    Re: Why does the location of PAD move around? Mark Wills <markwills1970@gmail.com> - 2017-04-02 08:29 -0700
  Re: Why does the location of PAD move around? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-02 04:13 -0500
    Re: Why does the location of PAD move around? Paul Rubin <no.email@nospam.invalid> - 2017-04-02 18:08 -0700
      Re: Why does the location of PAD move around? Julian Fondren <julian.fondren@gmail.com> - 2017-04-02 18:13 -0700
        Re: Why does the location of PAD move around? Paul Rubin <no.email@nospam.invalid> - 2017-04-02 18:22 -0700
          Re: Why does the location of PAD move around? Julian Fondren <julian.fondren@gmail.com> - 2017-04-02 18:31 -0700
          Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-03 04:37 +0200
            Re: Why does the location of PAD move around? Paul Rubin <no.email@nospam.invalid> - 2017-04-02 22:04 -0700
              Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 13:47 +0200
                Re: Why does the location of PAD move around? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-04 10:53 -0500
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-04 17:04 +0100
                Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 19:00 +0200
                Re: Why does the location of PAD move around? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-05 03:39 -0500
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-05 19:17 +0100
            Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-02 21:44 -1000
          Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-02 21:35 -1000
          Re: Why does the location of PAD move around? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-03 03:38 -0500
          Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-05 11:25 +1000
            Re: Why does the location of PAD move around? Paul Rubin <no.email@nospam.invalid> - 2017-04-05 18:23 -0700
              Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-07 14:26 +1000
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-07 08:47 +0100
                Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-08 10:25 +1000
                Re: Why does the location of PAD move around? Paul Rubin <no.email@nospam.invalid> - 2017-04-07 20:37 -0700
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-08 12:42 +0100
                Re: Why does the location of PAD move around? jason.songhurst@gmail.com - 2017-04-08 20:28 -0700
                Re: Why does the location of PAD move around? Coos Haak <htrofhc@gmail.com> - 2017-04-09 13:47 +0200
                Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-09 08:36 -1000
                Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-09 14:48 +0200
                Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-10 10:31 +1000
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-10 09:29 +0100
                Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-10 11:57 +0200
      Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-03 03:43 +0200
        Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-02 21:53 -1000
  Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-02 21:31 +1000
    Re: Why does the location of PAD move around? Coos Haak <htrofhc@gmail.com> - 2017-04-02 15:12 +0200
      Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-03 10:46 +1000
        Re: Why does the location of PAD move around? albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-03 03:31 +0200
          Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-02 19:14 -0700
        Re: Why does the location of PAD move around? "Elizabeth D. Rather" <erather@forth.com> - 2017-04-02 21:55 -1000
          Re: Why does the location of PAD move around? "HAA" <someone@microsoft.com> - 2017-04-04 11:06 +1000
            Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-04 12:54 +0100
              Re: Why does the location of PAD move around? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-04 16:27 +0000
                Re: Why does the location of PAD move around? Alex <alex@rivadpm.com> - 2017-04-04 19:23 +0100
          Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-07 22:04 -0700
    Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-02 14:21 -0700
  Why does the location of PAD move around? Mark Wills <markwills1970@gmail.com> - 2017-04-02 08:28 -0700
    Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-02 13:47 -0700
      Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-02 15:13 -0700
        Re: Why does the location of PAD move around? hughaguilar96@gmail.com - 2017-04-02 18:55 -0700

csiph-web