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

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Message-ID: <20070503101910.GB20142@gnuppy.monkey.org>
Date:	Thu, 3 May 2007 03:19:10 -0700
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	Ting Yang <tingy@...umass.edu>
Cc:	William Lee Irwin III <wli@...omorphy.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: [patch] CFS scheduler, -v8

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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