linux-kernel - Re: [PATCH (updated)] timer: Run calc_load halfway through each round

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Message-ID: <20070301231003.GD10643@holomorphy.com>
Date:	Thu, 1 Mar 2007 15:10:03 -0800
From:	Bill Irwin <bill.irwin@...cle.com>
To:	Simon Arlott <simon@...e.lp0.eu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, arjan@...ux.intel.com
Subject: Re: [PATCH (updated)] timer: Run calc_load halfway through each round_jiffies second

On Thu, Mar 01, 2007 at 10:52:01PM +0000, Simon Arlott wrote:
> Whenever jiffies is started at a multiple of 5*HZ or wraps, calc_load is 
> run exactly on the second which is when tasks using round_jiffies will 
> be scheduled to run. This has a bad effect on the load average, making 
> it tend towards 1.00 if a task happens to run every time the load is 
> being calculated.
> This changes calc_load so that it updates load half a second after any 
> tasks scheduled using round_jiffies.
> Signed-off-by: Simon Arlott <simon@...e.lp0.eu>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>

Well, it doesn't reintroduce the for_each_task() (not that it's present
in similar form) loop in count_active_tasks(), so it doesn't bother me.
You seem to have merely changed some offsets, which resolves the
round_jiffies() clash. It's easy to envision similar degenerate cases,
though I'm not sure we care enough to drop in a PRNG to handle them.


== wli
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