linux-kernel - Re: [patch] CFS scheduler, -v8

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Date:	Wed, 2 May 2007 12:10:33 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	"Li, Tong N" <tong.n.li@...el.com>
Cc:	tingy@...umass.edu, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] CFS scheduler, -v8

At some point in the past, Ting Yang wrote:
>>   Based on my understanding, adopting something like EEVDF in CFS should 
>> not be very difficult given their similarities, although I do not have 
>> any idea on how this impacts the load balancing for SMP. Does this worth 
>> a try?
>>   Sorry for such a long email :-)

On Wed, May 02, 2007 at 11:42:20AM -0700, Li, Tong N wrote:
> Thanks for the excellent explanation. I think EEVDF and many algs alike
> assume global ordering of all tasks in the system (based on virtual
> time), whereas CFS does so locally on each processor and relies on load
> balancing to achieve fairness across processors. It'd achieve strong
> fairness locally, but I'm not sure about its global fairness properties
> in an MP environment. If ideally the total load weight on each processor
> is always the same, then local fairness would imply global fairness, but
> this is a bin packing problem and is intractable ...

It's sort of obvious how to approximate it, but not entirely obvious
whether a given approximation actually suffices. More help with the
theoretical aspects is needed.


- wli
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