linux-kernel - Re: [ckrm-tech] [RFC] [PATCH 0/3] Add group fairness to CFS

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Message-ID: <20070531093622.GB9826@in.ibm.com>
Date:	Thu, 31 May 2007 15:06:22 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	ckrm-tech@...ts.sourceforge.net, efault@....de,
	Peter Williams <pwil3058@...pond.net.au>, tingy@...umass.edu,
	linux-kernel@...r.kernel.org, kernel@...ivas.org,
	tong.n.li@...el.com, containers@...ts.osdl.org,
	Ingo Molnar <mingo@...e.hu>, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, Guillaume Chazarain <guichaz@...oo.fr>
Subject: Re: [ckrm-tech] [RFC] [PATCH 0/3] Add group fairness to CFS

On Thu, May 31, 2007 at 02:15:34AM -0700, William Lee Irwin III wrote:
> Yes, the larger number of schedulable entities and hence slower
> convergence to groupwise weightings is a disadvantage of the flattening.
> A hybrid scheme seems reasonable enough. 

Cool! This puts me back on track to implement hierarchical scheduling in
CFS :)

Once this is done and once I can get containers running on a box, I will 
experiment with the flattening trick for user and process levels inside 
containers.

Thanks for your feedback so far!

> Ideally one would chop the
> hierarchy in pieces so that n levels of hierarchy become k levels of n/k
> weight-flattened hierarchies for this sort of attack to be most effective
> (at least assuming similar branching factors at all levels of hierarchy
> and sufficient depth to the hierarchy to make it meaningful) but this is
> awkward to do. Peeling off the outermost container or whichever level is
> deemed most important in terms of accuracy of aggregate enforcement as
> a hierarchical scheduler is a practical compromise.
> 
> Hybrid schemes will still incur the difficulties of hierarchical
> scheduling, but they're by no means insurmountable. Sadly, only
> complete flattening yields the simplifications that make task group
> weighting enforcement orthogonal to load balancing and the like. The
> scheme I described for global nice number behavior is also not readily
> adaptable to hybrid schemes.

-- 
Regards,
vatsa
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