A question about CFS

[Shachar Shemesh]

Oleg Goldshmidt wrote:
>
> Yes, as in O(1). The implementation of the runqueue has changed in
> CFS.
>   
You are hinting that between the run queues nothing has changed. That 
seem unlikely to me.
>  
>   
>> If so, how do the relative priorities happen?
>>     
>
> I am not sure what you mean by "relative priorities". Do you mean,
> "niceness"?
Yes. One of the things said about CFS was that with it things that 
previously required real time priority now can run at nice -20 just as well.

That same text (I don't remember right now where I read it, nor who 
wrote it) said that CFS fixed a nice anomality that used to exist with 
O(1). Apparently, two adjacent nice levels are supposed to have a more 
or less fixed CPU spread between them, no matter what the absolute nice 
level is (the article suggested that if the system has just two 
processes, one at nice level X and another at nice X+1, then the CPU 
should be divided 45-55 between them). It was suggested that O(1) had 
non-linear nice graph, due to the tricks played to make nice -20 
approximate what it should do.
>
> Only ready or running processes are scheduled - others don't even want
> the CPU.
>
>   
Being as it is that the load average on my system rarely goes above 4, I 
can see why nobody is worried about O(log n).

Thanks,
Shachar

-- 
Shachar Shemesh
Lingnu Open Source Consulting Ltd.
http://www.lingnu.com

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