On Sun, Apr 18, 2010 at 09:35:42PM +0800, Aaron Lewis wrote:
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> Hi,
> I'm reading Operating System Concepts (7th Edition) , Written by
> Abraham , Peter & Greg.
>
> In chapter 5.3 , it talks about a schedule algorithm: SJF
> SJF means shortest jobs schedules firstly.
>
> To compare different process , thy use a process running time.
>
> e.g
> P1 takes 6 secs to run
> P2 takes 3 seconds
> P3 takes 10 secs
>
> Then we should put those tasks in array like this:
> P2 => P1 => P3
>
> That looks much reasonable , but my question is , how does an OS know
> that a process will takes longer time to finish its life ?
> I think it's impossible to let OS know exactly how long a process will
> take to run.
>
>
> So far in my experience , i think there's a few ways to compare
> Process running time:
>
> Forgive me if i have a poor experience on OS ;-)
>
> I) Number of Loops in a Program , can be detected by compiler
> As long as you have any loops , you are slower than any straight ahead
> program
>
> II) Length of Program , longer code takes longer time sometimes , not a
> good way.
>
>
> Anyone wants to share some experience with me ?
You cannot tell in general, that's a basic result from CS. But you can
measure previous runs and do predictions based on that, in some cases
at least. I hope I'm not answering a homework assignment...
-Otto
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> Be very glad to hear your voice ;-)
>
>
>
> - --
> Best Regards,
> Aaron Lewis - PGP: 0x4A6D32A0
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