Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

From	Juri Lelli <juri.lelli@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
Date	2017-08-21 16:10 +0200
Message-ID	<ugVyX-5o7-37@gated-at.bofh.it> (permalink)
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On 21/08/17 15:56, Peter Zijlstra wrote:
> On Mon, Aug 21, 2017 at 02:44:58PM +0100, Juri Lelli wrote:
> 
> > Also, I'm not sure what Peter meant with
> > 
> > "But still this isn't quite right, because when we consider this for SMT
> > (as was the intent here) we'll happily occupy a full sibling core over
> > finding an empty one."
> 
> Consider a 4 core, SMT2 system:
> 
> LLC	[0         -         7]
> 
> SMT	[0,1] [2,3] [4,5] [6,7]
> 
> If we do a wake-up on CPU0, we'll find CPU1, mark that as fallback,
> continue up the domain tree, exclude 0,1 from 0-7 and find CPU2.
> 
> A next wakeup on CPU0 does the same and will find CPU3, fully loading
> that core, instead of considering CPU4 first.
> 

Ah, right, I see. Thanks for explaining.

Byungchul, maybe you could add this explanation as a comment?

> Doing this 'right' is difficult and expensive :-/
>

Thread

[PATCH v8 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-08-18 10:30 +0200
  [PATCH v8 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-18 10:30 +0200
    Re: [PATCH v8 2/2] sched/rt: Add support for SD_PREFER_SIBLING on  find_lowest_rq() Steven Rostedt <rostedt@goodmis.org> - 2017-08-18 15:40 +0200
  [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-18 10:30 +0200
    Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Juri Lelli <juri.lelli@arm.com> - 2017-08-21 15:50 +0200
      Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Peter Zijlstra <peterz@infradead.org> - 2017-08-21 16:00 +0200
        Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Juri Lelli <juri.lelli@arm.com> - 2017-08-21 16:10 +0200
          Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-22 08:00 +0200
      Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-22 08:00 +0200
        Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-22 09:20 +0200
        Re: [PATCH v8 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Juri Lelli <juri.lelli@arm.com> - 2017-08-22 09:50 +0200

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