From: Peter Zijlstra <peterz@infradead.org>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>, Ingo Molnar <mingo@kernel.org>,
linux-man <linux-man@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: RFC: documentation of the autogroup feature [v2]
Date: Tue, 29 Nov 2016 12:46:29 +0100 [thread overview]
Message-ID: <20161129114629.GG3092@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <755aba1b-9bf4-0277-0628-b27e725ee2f9@gmail.com>
On Tue, Nov 29, 2016 at 08:43:33AM +0100, Michael Kerrisk (man-pages) wrote:
> >
> > In any case, for the case of autogroup, the behaviour has always been,
> > autogroups came quite late.
>
> This ("the behavior has always been") isn't quite true. Yes, group
> scheduling has been around since Linux 2.6.24, but in terms of the
> semantics of the thread nice value, there was no visible change
> then, *unless* explicit action was taken to create cgroups.
>
> The arrival of autogroups in Linux 2.6.38 was different.
> With this feature enabled (which is the default), task
I don't think the SCHED_AUTOGROUP symbol is default y, most distros
might have default enabled it, but that's not something I can help.
> groups were implicitly created *without the user needing to
> do anything*. Thus, [two terminal windows] == [two task groups]
> and in those two terminal windows, nice(1) on a CPU-bound
> command in one terminal did nothing in terms of improving
> CPU access for a CPU-bound tasks running on the other terminal
> window.
>
> Put more succinctly: in Linux 2.6.38, autogrouping broke nice(1)
> for many use cases.
>
> Once I came to that simple summary it was easy to find multiple
> reports of problems from users:
>
> http://serverfault.com/questions/405092/nice-level-not-working-on-linux
> http://superuser.com/questions/805599/nice-has-no-effect-in-linux-unless-the-same-shell-is-used
> https://www.reddit.com/r/linux/comments/1c4jew/nice_has_no_effect/
> http://stackoverflow.com/questions/10342470/process-niceness-priority-setting-has-no-effect-on-linux
>
> Someone else quickly pointed out to me another such report:
>
> https://bbs.archlinux.org/viewtopic.php?id=149553
Well, none of that ever got back to me, so again, nothing I could do
about that.
> And when I quickly surveyed a few more or less savvy Linux users
> in one room, most understood what nice does, but none of them knew
> about the behavior change wrought by autogroup.
>
> I haven't looked at all of the mails in the old threads that
> discussed the implementation of this feature, but so far none of
> those that I saw mentioned this behavior change. It's unfortunate
> that it never even got documented.
Well, when we added the feature people (most notable Linus) understood
what cgroups did. So no surprises for any of us.
next prev parent reply other threads:[~2016-11-29 11:47 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-22 15:59 RFC: documentation of the autogroup feature Michael Kerrisk (man-pages)
2016-11-23 10:33 ` [patch] sched/autogroup: Fix 64bit kernel nice adjustment Mike Galbraith
2016-11-23 13:47 ` Michael Kerrisk (man-pages)
2016-11-23 14:12 ` Mike Galbraith
2016-11-23 14:20 ` Michael Kerrisk (man-pages)
2016-11-23 15:55 ` Mike Galbraith
2016-11-24 6:24 ` [tip:sched/urgent] sched/autogroup: Fix 64-bit kernel nice level adjustment tip-bot for Mike Galbraith
2016-11-23 11:39 ` RFC: documentation of the autogroup feature Mike Galbraith
2016-11-23 13:54 ` Michael Kerrisk (man-pages)
2016-11-23 15:33 ` Mike Galbraith
2016-11-23 16:04 ` Michael Kerrisk (man-pages)
2016-11-23 17:11 ` Mike Galbraith
2016-11-24 21:41 ` RFC: documentation of the autogroup feature [v2] Michael Kerrisk (man-pages)
2016-11-25 12:52 ` Afzal Mohammed
2016-11-25 13:04 ` Michael Kerrisk (man-pages)
2016-11-25 13:02 ` Mike Galbraith
2016-11-25 15:04 ` Michael Kerrisk (man-pages)
2016-11-25 15:48 ` Michael Kerrisk (man-pages)
2016-11-25 15:51 ` Mike Galbraith
2016-11-25 16:08 ` Michael Kerrisk (man-pages)
2016-11-25 16:18 ` Peter Zijlstra
2016-11-25 16:34 ` Michael Kerrisk (man-pages)
2016-11-25 20:54 ` Michael Kerrisk (man-pages)
2016-11-25 21:49 ` Peter Zijlstra
2016-11-29 7:43 ` Michael Kerrisk (man-pages)
2016-11-29 11:46 ` Peter Zijlstra [this message]
2016-11-29 13:44 ` Michael Kerrisk (man-pages)
2016-11-25 16:04 ` Peter Zijlstra
2016-11-25 16:13 ` Peter Zijlstra
2016-11-25 16:33 ` Michael Kerrisk (man-pages)
2016-11-25 22:48 ` Peter Zijlstra
2016-11-23 16:05 ` RFC: documentation of the autogroup feature Michael Kerrisk (man-pages)
2016-11-23 17:19 ` Mike Galbraith
2016-11-23 22:12 ` Michael Kerrisk (man-pages)
2016-11-27 21:13 ` Michael Kerrisk (man-pages)
2016-11-28 1:46 ` Mike Galbraith
[not found] ` <1127218a-dd9b-71a8-845d-3a83969632fc@gmail.com>
2016-11-29 9:10 ` Michael Kerrisk (man-pages)
2016-11-29 13:46 ` Mike Galbraith
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