linux-kernel - Re: [PATCH] sched: fix off-by-one bug in balance

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Message-ID: <49E6887D.6030400@cn.fujitsu.com>
Date:	Thu, 16 Apr 2009 09:23:09 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: fix off-by-one bug in balance_tasks()

on 2009-4-15 19:41 Peter Zijlstra wrote:
> On Wed, 2009-04-15 at 10:49 +0800, Miao Xie wrote:
>> If the load that need be moved equals the half weight of a task, I think
>> it is unnecessary to move this task. Or this task will be moved back and
>> forth.
> 
> That's actually desirable. Consider the 3 tasks on 2 cpus statically
> infeasible scenario. There you'd want the tasks to bounce around a bit
> in order to provide fairness.

I see. Thanks for your explanation.

Miao Xie
> 
>> Signed-off-by: Miao Xie <miaox@...fujitsu.com>
>> ---
>>  kernel/sched.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/sched.c b/kernel/sched.c
>> index 5724508..44926c8 100644
>> --- a/kernel/sched.c
>> +++ b/kernel/sched.c
>> @@ -3085,7 +3085,7 @@ next:
>>  	if (!p || loops++ > sysctl_sched_nr_migrate)
>>  		goto out;
>>  
>> -	if ((p->se.load.weight >> 1) > rem_load_move ||
>> +	if ((p->se.load.weight >> 1) >= rem_load_move ||
>>  	    !can_migrate_task(p, busiest, this_cpu, sd, idle, &pinned)) {
>>  		p = iterator->next(iterator->arg);
>>  		goto next;
> 
> 
> 
> 


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