Date: Thu, 3 May 2007 03:19:10 -0700
To: Ting Yang <tingy@cs.umass.edu>
Cc: William Lee Irwin III <wli@holomorphy.com>,
       Srivatsa Vaddagiri <vatsa@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org,
       "Bill Huey (hui)" <billh@gnuppy.monkey.org>
Subject: Re: [patch] CFS scheduler, -v8
Message-ID: <20070503101910.GB20142@gnuppy.monkey.org>
References: <20070501212223.GA29867@elte.hu> <4637FE0A.7090405@cs.umass.edu> <20070502173634.GA11308@in.ibm.com> <20070502174829.GX19966@holomorphy.com> <46395495.3020802@cs.umass.edu>
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From: Bill Huey (hui) <billh@gnuppy.monkey.org>
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On Wed, May 02, 2007 at 11:18:45PM -0400, Ting Yang wrote:
> I just want to point out that ->wait_runtime, in fact, stores the lag of 
> each task in CFS, except that it is also used by other things, and 
> occasionally tweaked (heuristically ?). Under normal cases the sum of 
> lags of all active tasks in such a system, should be a constant 0. The 
> lag information is equally important to EEVDF, when some tasks leave the 
> system (becomes inactive) carrying certain amount of lag. The key point 
> here is that we have to spread the lag (either negative or positive) to 
> all remaining task, so that the fairness of the system is preserved. I 
> thinks CFS implementation does not seems to handle this properly.
> 
> I am running out time today :-( I will write an email about CFS -v8 
> tomorrow, describing 2 issues in CFS I found related to this.

Interesting. I haven't look at the code carefully but that wouldn't
surprise me if this was the case and it led to odd corner cases.

I'm eagerly waiting your analysis and explanation.

bill

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