linux-kernel - Re: fair clock use in CFS

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Message-ID: <20070514150234.GB6103@in.ibm.com>
Date:	Mon, 14 May 2007 20:32:34 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Daniel Hazelton <dhazelton@...er.net>
Cc:	Ingo Molnar <mingo@...e.hu>,
	William Lee Irwin III <wli@...omorphy.com>, efault@....de,
	tingy@...umass.edu, linux-kernel@...r.kernel.org
Subject: Re: fair clock use in CFS

On Mon, May 14, 2007 at 10:31:13AM -0400, Daniel Hazelton wrote:
> Hrm... Okay, so you're saying that "fair_clock" runs slower the more process 
> there are running to keep the above run-up in "Time Spent on CPU" I noticed 
> based solely on your initial example? If that is the case, then I can see the 
> fairness - its just not visible from a really quick look at the code and the 
> simplified description you gave earlier.

>From the code:

update_curr() 

        delta_fair = delta_exec * NICE_0_LOAD;
        do_div(delta_fair, rq->raw_weighted_load);

	..

	rq->fair_clock += delta_fair;

Although wall clock would have advanced by delta_exec, fair clock
advances only by delta_fair.

More the load on the CPU (rq->raw_weighted_load), slower is this advance
compared to wall clock.



-- 
Regards,
vatsa
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