linux-kernel - Re: [PATCH v10 10/11] sched: add SD_PREFER

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Date:	Mon, 23 Mar 2015 15:29:58 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>
CC:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v10 10/11] sched: add SD_PREFER_SIBLING for SMT level



On 03/23/2015 02:41 PM, Peter Zijlstra wrote:
> On Tue, Mar 03, 2015 at 09:38:11AM +0100, Vincent Guittot wrote:
> 
>>> Prefer siblings logic dates back to https://lkml.org/lkml/2009/8/27/210
>>> and only used in update_sd_lb_stats() where we have
>>>
>>> if (child && child->flags & SD_PREFER_SIBLING)
>>>          prefer_sibling = 1;
>>>
>>> However what confuses me is why should we even look at a child domain's
>>> flag to balance tasks across the current sched domain? Why cant we just
>>> set and use a sd flag at current level than to look at child domain
>>> flag?
>>
>> Peter,
>> have you got some insight about the reason ?
> 
> Yeah, because it makes sense that way? ;-)
> 
> The we want to move things to the child's sibling, not the parent's
> sibling. We further need to have a child for this to make sense.
> 
> 

+1. The above is precisely why we need this patch.

Regards
Preeti U Murthy

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