linux-kernel - Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later

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Message-ID: <20170816140414.GW20323@X58A-UD3R>
Date:   Wed, 16 Aug 2017 23:04:14 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, juri.lelli@...il.com,
        kernel-team@....com
Subject: Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING
 on find_later_rq()

On Wed, Aug 16, 2017 at 09:32:44AM -0400, Steven Rostedt wrote:
> On Wed, 16 Aug 2017 11:17:36 +0900
> Byungchul Park <byungchul.park@....com> wrote:
> 
> 
> > Yes, that's what I intended. IOW:
> > 
> > If (we found a proper sd, not having SD_PREFER_SIBLING?)
> > 	use the sd;
> > else if (we found a proper sd, having SD_PREFER_SIBLING?)
> > 	use the smallest sd among SD_PREFER_SIBLING sds;
> 
> BTW, what do you mean by "smallest sd"?

There might be more than one SD_PREFER_SIBLING domain in its hierachy.
In that case, we have to choose one of them. Imagine the following
example, in case that the source cpu is cpu 0:

[Domain hierachy for cpu 0]

cpu 0 -+ domain 1                 -+
       | SD_PREFER_SIBLING flaged  |
cpu 1 -+                           +- domain 2
                                   |  SD_PREFER_SIBLING flaged
cpu 2 -+---------------------------+
       |
cpu 3 -+

In this case, we have to choose domain 1 than 2, because cpus in domain 1
are closer to the source cpu, cpu 0. That's what I meant.