linux-kernel - Re: fair group scheduler not so fair?

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Message-Id: <1211535561.6463.184.camel@lappy.programming.kicks-ass.net>
Date:	Fri, 23 May 2008 11:39:21 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	vatsa@...ux.vnet.ibm.com
Cc:	"Li, Tong N" <tong.n.li@...el.com>,
	Chris Friesen <cfriesen@...tel.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, pj@....com
Subject: Re: fair group scheduler not so fair?

On Fri, 2008-05-23 at 15:12 +0530, Srivatsa Vaddagiri wrote:
> On Thu, May 22, 2008 at 01:18:33PM -0700, Li, Tong N wrote:
> > Peter,
> > 
> > I didn't look at your patches, but I thought you were flattening group
> > weights down to task-level so that the scheduler only looks at per-task
> > weights.
> 
> Wouldnt that require task weight readjustment upon every fork/exit?

If you were to do that - yes that would get you into some very serious
trouble.

The route I've chosen is to basically recompute it every time I need the
weight. So every time I use a weight, I do:

  \Prod_{l=1} w_l/rw_{l-1}

Not doing that will get you O(n) recomputes on all sorts of situations.


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