From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 11D5A7DE69 for ; Fri, 12 Oct 2018 17:57:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727500AbeJMBaW (ORCPT ); Fri, 12 Oct 2018 21:30:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35710 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727051AbeJMBaW (ORCPT ); Fri, 12 Oct 2018 21:30:22 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D098080F7D; Fri, 12 Oct 2018 17:56:42 +0000 (UTC) Received: from llong.com (dhcp-17-8.bos.redhat.com [10.18.17.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 268EC82779; Fri, 12 Oct 2018 17:56:41 +0000 (UTC) From: Waiman Long To: Tejun Heo , Li Zefan , Johannes Weiner , Peter Zijlstra , Ingo Molnar Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@fb.com, pjt@google.com, luto@amacapital.net, Mike Galbraith , torvalds@linux-foundation.org, Roman Gushchin , Juri Lelli , Patrick Bellasi , Waiman Long Subject: [PATCH v13 10/11] cpuset: Add documentation about the new "cpuset.sched.partition" flag Date: Fri, 12 Oct 2018 13:55:50 -0400 Message-Id: <1539366951-8498-11-git-send-email-longman@redhat.com> In-Reply-To: <1539366951-8498-1-git-send-email-longman@redhat.com> References: <1539366951-8498-1-git-send-email-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 12 Oct 2018 17:56:43 +0000 (UTC) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org The cgroup-v2.rst file is updated to document the purpose of the new "cpuset.sched.partition" flag and how its usage. Signed-off-by: Waiman Long --- Documentation/admin-guide/cgroup-v2.rst | 66 +++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 533e85c..178cda4 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1686,6 +1686,72 @@ Cpuset Interface Files Its value will be affected by memory nodes hotplug events. + cpuset.sched.partition + A read-write single value file which exists on non-root + cpuset-enabled cgroups. It accepts either "0" (off) or "1" + (on) when written to. This flag is set and owned by the + parent cgroup. + + If set, it indicates that the current cgroup is the root of a + new partition or scheduling domain that comprises itself and + all its descendants except those that are separate partition + roots themselves and their descendants. The root cgroup is + always a partition root. + + There are constraints on where this flag can be set. It can + only be set in a cgroup if all the following conditions are true. + + 1) The "cpuset.cpus" is not empty and the list of CPUs are + exclusive, i.e. they are not shared by any of its siblings. + 2) The parent cgroup is a partition root. + 3) The "cpuset.cpus" is also a proper subset of the parent's + "cpuset.cpus.effective". + 4) There is no child cgroups with cpuset enabled. This is for + eliminating corner cases that have to be handled if such a + condition is allowed. + + Setting this flag will take the CPUs away from the effective + CPUs of the parent cgroup. Once it is set, this flag cannot + be cleared if there are any child cgroups with cpuset enabled. + + A parent partition cannot distribute all its CPUs to its + child partitions. There must be at least one cpu left in the + parent partition. + + Once becoming a partition root, changes to "cpuset.cpus" is + generally allowed as long as the first condition above is true, + the change will not take away all the CPUs from the parent + partition and the new "cpuset.cpus" value is a superset of its + children's "cpuset.cpus" values. + + Sometimes, external factors like changes to ancestors' + "cpuset.cpus" or cpu hotplug can cause the state of the partition + root to change. On read, the "cpuset.sched.partition" file + can show the following values. + + "0" Not a partition root + "1" Partition root + "-1" Erroneous partition root + + It is a partition root if the first 2 partition root conditions + above are true and at least one CPU from "cpuset.cpus" is + granted by the parent cgroup. + + A partition root can become an erroneous partition root if none + of CPUs requested in "cpuset.cpus" can be granted by the parent + cgroup or the parent cgroup is no longer a partition root. + In this case, it is not a real partition even though the + restriction of the first partition root condition above will + still apply. All the tasks in the cgroup will be migrated to + the nearest ancestor partition. + + An erroneous partition root can be transitioned back to a real + partition root if at least one of the requested CPUs can now be + granted by its parent. In this case, the tasks will be migrated + back to the newly created partition. Clearing the partition + flag of an erroneous partition root is always allowed even if + child cpusets are present. + Device controller ----------------- -- 1.8.3.1