linux-kernel - Re: [PATCH 09/10] sched, fair: Fix the sd_parent

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Message-ID: <CAPM31RJmV1vhcpUJ8s1mmB-F9z__TRj+BuxjYkPFd75zkudwvg@mail.gmail.com>
Date:	Tue, 27 Aug 2013 02:05:06 -0700
From:	Paul Turner <pjt@...gle.com>
To:	Rik van Riel <riel@...riel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Lei Wen <leiwen@...vell.com>, Joonsoo Kim <js1304@...il.com>
Subject: Re: [PATCH 09/10] sched, fair: Fix the sd_parent_degenerate() code

On Mon, Aug 26, 2013 at 2:49 PM, Rik van Riel <riel@...riel.com> wrote:
> On 08/26/2013 08:09 AM, Peter Zijlstra wrote:
>> On Sat, Aug 24, 2013 at 03:45:57AM -0700, Paul Turner wrote:
>>>> @@ -5157,6 +5158,13 @@ cpu_attach_domain(struct sched_domain *s
>>>>                         tmp->parent = parent->parent;
>>>>                         if (parent->parent)
>>>>                                 parent->parent->child = tmp;
>>>> +                       /*
>>>> +                        * Transfer SD_PREFER_SIBLING down in case of a
>>>> +                        * degenerate parent; the spans match for this
>>>> +                        * so the property transfers.
>>>> +                        */
>>>> +                       if (parent->flags & SD_PREFER_SIBLING)
>>>> +                               tmp->flags |= SD_PREFER_SIBLING;
>>>>                         destroy_sched_domain(parent, cpu);
>>>>                 } else
>>>>                         tmp = tmp->parent;
>>>>
>>>
>>> Reviewed-by: Paul Turner <pjt@...gle.com>
>>
>> BTW, did that comment make sense to you or would you suggest something
>> different? I had/am having a hard time with that comment. Somehow it
>> leaves me wanting. I know I understand the issue now, but I'll doubt the
>> comment will suffice in a years time :/
>
> The comment made sense to me :)

It makes sense once you read the code.  That we push down is somehow
counter intuitive in the reading.

>
> --
> All rights reversed.
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