From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Mike Galbraith <efault@gmx.de>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
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
Date: Tue, 29 Nov 2016 10:10:22 +0100 [thread overview]
Message-ID: <CAKgNAkiLafr7KJNAo+_kwKQB7ueO-oontNL_FQrGtqitmJpEDg@mail.gmail.com> (raw)
In-Reply-To: <1127218a-dd9b-71a8-845d-3a83969632fc@gmail.com>
[Resending because of bounces from the lists. (Somehow my mailer
messed up the MIME labeling)]
Hi Mike,
On 11/28/2016 02:46 AM, Mike Galbraith wrote:
> On Sun, 2016-11-27 at 22:13 +0100, Michael Kerrisk (man-pages) wrote:
>
>> Here's my attempt to define the root task group:
>>
>> * If autogrouping is disabled, then all processes in the root CPU
>> cgroup form a scheduling group (sometimes called the "root task
>> group").
>>
>> Can you improve on this?
The below is helpful, but...
> A task group is a set of percpu runqueues.
The explanation needs really to be in terms of what user-space
understands and sees. "Runqueues" are a kernel scheduler implementation
detail.
> The root task group is the
> top level set in a hierarchy of such sets when group scheduling is
> enabled, or the only set when group scheduling is not enabled. The
> autogroup hierarchy has a depth of one, ie all autogroups are peers
> who's common parent is the root task group.
Let's try and go further. How's this:
When scheduling non-real-time processes (i.e., those scheduled
under the SCHED_OTHER, SCHED_BATCH, and SCHED_IDLE policies), the
CFS scheduler employs a technique known as "group scheduling", if
the kernel was configured with the CONFIG_FAIR_GROUP_SCHED option
(which is typical).
Under group scheduling, threads are scheduled in "task groups".
Task groups have a hierarchical relationship, rooted under the
initial task group on the system, known as the "root task group".
Task groups are formed in the following circumstances:
* All of the threads in a CPU cgroup form a task group. The par‐
ent of this task group is the task group of the corresponding
parent cgroup.
* If autogrouping is enabled, then all of the threads that are
(implicitly) placed in an autogroup (i.e., the same session, as
created by setsid(2)) form a task group. Each new autogroup is
thus a separate task group. The root task group is the parent
of all such autogroups.
* If autogrouping is enabled, then the root task group consists
of all processes in the root CPU cgroup that were not otherwise
implicitly placed into a new autogroup.
* If autogrouping is disabled, then the root task group consists
of all processes in the root CPU cgroup.
* If group scheduling was disabled (i.e., the kernel was config‐
ured without CONFIG_FAIR_GROUP_SCHED), then all of the pro‐
cesses on the system are notionally placed in a single task
group.
[To be followed by a discussion of the nice value and task groups]
?
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2016-11-29 9:11 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
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) [this message]
2016-11-29 13:46 ` Mike Galbraith
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