linux-kernel - Re: [PATCH] sched: fair-group: fix a Div0 error of the fair group scheduler

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Message-Id: <1209371625.13978.1.camel@twins>
Date:	Mon, 28 Apr 2008 10:33:45 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	miaox@...fujitsu.com
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: fair-group: fix a Div0 error of the fair group
	scheduler

On Mon, 2008-04-28 at 16:27 +0800, Miao Xie wrote:

> I'm sorry, I didn't explained clearly.Though echoing ULONG_MAX value into
> cpu.shares causes Div0 error, this error was not caused by the above code.
> It is caused by the following code.
> 
>     calc_delta_mine()
>         ->lw->inv_weight = (WMULT_CONST-lw->weight/2) / (lw->weight+1);
> 
> And besides, the Div0 error caused by echoing ULONG_MAX occured on the UP system
> or on SMP system with only one cpu.
> 
> So this patch fixes the bug caused by echoing a number which was less than the number
> of processores into the "cpu.shares" file, but doesn't fix the bug caused by echoing
> ULONG_MAX.

Ah, ok. But I guess we run into other problems with weights that heavy,
but we should not crash.

Ok, I'll ACK your initial patch

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