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Date: Mon, 23 Mar 2015 15:29:58 +0530
From: Preeti U Murthy <preeti@linux.vnet.ibm.com>
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To: Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>
CC: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>, Mike Galbraith <efault@gmx.de>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Linaro Kernel Mailman List <linaro-kernel@lists.linaro.org>
Subject: Re: [PATCH v10 10/11] sched: add SD_PREFER_SIBLING for SMT level
References: <1425052454-25797-1-git-send-email-vincent.guittot@linaro.org> <1425052454-25797-11-git-send-email-vincent.guittot@linaro.org> <20150302115249.GA9875@linux.vnet.ibm.com> <CAKfTPtBOYOuB8sj2mMCEsBSZZ+KoSr+bkQLvAKHPTSWTbtzM0g@mail.gmail.com> <20150323091152.GC23123@twins.programming.kicks-ass.net>
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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