Subject: Re: A nice CPU resource controller
From: Mike Galbraith <efault@gmx.de>
To: Martin Ohlin <martin.ohlin@control.lth.se>
Cc: Peter Williams <pwil3058@bigpond.net.au>, balbir@in.ibm.com,
       linux-kernel@vger.kernel.org
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Date: Thu, 31 Aug 2006 14:17:43 +0000
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On Thu, 2006-08-31 at 12:35 +0200, Martin Ohlin wrote:
> Mike Galbraith wrote:
> > On Thu, 2006-08-31 at 06:53 +0000, Mike Galbraith wrote:
> >> On Thu, 2006-08-31 at 11:07 +1000, Peter Williams wrote:
> >>
> >>> But your implication here is valid.  It is better to fiddle with the 
> >>> dynamic priorities than with nice as this leaves nice for its primary 
> >>> purpose of enabling the sysadmin to effect the allocation of CPU 
> >>> resources based on external considerations.
> >> I don't understand.  It _is_ the administrator fiddling with nice based
> >> on external considerations.  It just steadies the administrator's hand.
> > 
> > When extended to groups, I see your point.  The admin would lose his
> > ability to apportion bandwidth _within_ the group because he's already
> > turned his only knob.  That is going to be just as much of a problem for
> > other methods though, and is just a question of how much complexity you
> > want to pay to achieve fine grained control.
> 
> I do not see the problem. Let's say I create a group of three tasks and 
> give it 50% of the CPU bandwidth (perhaps by using the same nice value 
> for all the tasks in this group). If I then want to apportion the 
> bandwidth within the group as you say, then the same thing can be done 
> by treating them as individual tasks.

Multiplex nice?  (oh my, dig foxhole)

> Maybe I am wrong, but as I see it, if one wants to control on a group 
> level, then the individual shares within the group are not that 
> important. If the individual share is important, then it should be 
> controlled on a per-task level. Please tell me if I am wrong.

That's probably right 99% of the time.

	-Mike

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