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Re: RFC: documentation of the autogroup feature [v2]

From Mike Galbraith <efault@gmx.de>
Newsgroups linux.kernel
Subject Re: RFC: documentation of the autogroup feature [v2]
Date 2016-11-25 17:00 +0100
Message-ID <sHr4R-2rt-3@gated-at.bofh.it> (permalink)
References (4 earlier) <sGIhs-71P-35@gated-at.bofh.it> <sGJnb-7Id-17@gated-at.bofh.it> <sHa41-8qT-7@gated-at.bofh.it> <sHoJH-15u-7@gated-at.bofh.it> <sHqBQ-2hw-27@gated-at.bofh.it>
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On Fri, 2016-11-25 at 16:04 +0100, Michael Kerrisk (man-pages) wrote:

> > >        ┌─────────────────────────────────────────────────────┐
> > >        │FIXME                                                │
> > >        ├─────────────────────────────────────────────────────┤
> > >        │How do the nice value of  a  process  and  the  nice │
> > >        │value of an autogroup interact? Which has priority?  │
> > >        │                                                     │
> > >        │It  *appears*  that the autogroup nice value is used │
> > >        │for CPU distribution between task groups,  and  that │
> > >        │the  process nice value has no effect there.  (I.e., │
> > >        │suppose two  autogroups  each  contain  a  CPU-bound │
> > >        │process,  with  one  process  having nice==0 and the │
> > >        │other having nice==19.  It appears  that  they  each │
> > >        │get  50%  of  the CPU.)  It appears that the process │
> > >        │nice value has effect only with respect to  schedul‐ │
> > >        │ing  relative to other processes in the *same* auto‐ │
> > >        │group.  Is this correct?                             │
> > >        └─────────────────────────────────────────────────────┘
> > 
> > Yup, entity nice level affects distribution among peer entities.
> 
> Huh! I only just learned about this via my experiments while
> investigating autogroups. 
> 
> How long have things been like this? Always? (I don't think
> so.) Since the arrival of CFS? Since the arrival of
> autogrouping? (I'm guessing not.) Since some other point?
> (When?)

Always.  Before CFS there just were no non-peers :)

> It seems to me that this renders the traditional process
> nice pretty much useless. (I bet I'm not the only one who'd 
> be surprised by the current behavior.)

Yup, group scheduling is not a single edged sword, those don't exist. 
 Box wide nice loss is not the only thing that can bite you, fairness,
whether group or task oriented cuts both ways.

	-Mike

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RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-22 17:20 +0100
  [patch] sched/autogroup: Fix 64bit kernel nice adjustment Mike Galbraith <efault@gmx.de> - 2016-11-23 11:40 +0100
    Re: [patch] sched/autogroup: Fix 64bit kernel nice adjustment "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 14:50 +0100
      Re: [patch] sched/autogroup: Fix 64bit kernel nice adjustment Mike Galbraith <efault@gmx.de> - 2016-11-23 15:20 +0100
        Re: [patch] sched/autogroup: Fix 64bit kernel nice adjustment "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 15:30 +0100
          Re: [patch] sched/autogroup: Fix 64bit kernel nice adjustment Mike Galbraith <efault@gmx.de> - 2016-11-23 17:00 +0100
    [tip:sched/urgent] sched/autogroup: Fix 64-bit kernel nice level  adjustment tip-bot for Mike Galbraith <tipbot@zytor.com> - 2016-11-24 07:30 +0100
  Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-23 12:50 +0100
    Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 15:00 +0100
      Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-23 16:40 +0100
        Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 17:10 +0100
          Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-23 18:20 +0100
            Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 23:50 +0100
        Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-23 17:10 +0100
          Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-23 18:20 +0100
            RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-24 22:50 +0100
              Re: RFC: documentation of the autogroup feature [v2] Afzal Mohammed <afzal.mohd.ma@gmail.com> - 2016-11-25 14:00 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 14:10 +0100
              Re: RFC: documentation of the autogroup feature [v2] Mike Galbraith <efault@gmx.de> - 2016-11-25 14:30 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 16:30 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 16:50 +0100
                Re: RFC: documentation of the autogroup feature [v2] Mike Galbraith <efault@gmx.de> - 2016-11-25 17:00 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 17:20 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-25 17:20 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 17:40 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 22:00 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-25 22:50 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-29 08:50 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-29 12:50 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-29 14:50 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-25 17:10 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-25 17:20 +0100
                Re: RFC: documentation of the autogroup feature [v2] "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-25 17:40 +0100
                Re: RFC: documentation of the autogroup feature [v2] Peter Zijlstra <peterz@infradead.org> - 2016-11-25 23:50 +0100
        Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-27 22:20 +0100
          Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-28 02:50 +0100
            Re: RFC: documentation of the autogroup feature "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-29 10:20 +0100
              Re: RFC: documentation of the autogroup feature Mike Galbraith <efault@gmx.de> - 2016-11-29 14:50 +0100

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