From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EF6EC4338F for ; Wed, 11 Aug 2021 03:07:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2D9E60E78 for ; Wed, 11 Aug 2021 03:07:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233751AbhHKDH1 (ORCPT ); Tue, 10 Aug 2021 23:07:27 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:25978 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233373AbhHKDHQ (ORCPT ); Tue, 10 Aug 2021 23:07:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628651212; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=AVbVzxNS1YmsKnryyA9yHoVdTcnd9W0dJr55HTJoU+Y=; b=Fyz46cIPbVNlNOMdZCo/tyLVGXBdcRxCTTvPXK7b4Zy68S/tWTxeX9AHZsKfjd29haaIt4 ecpwSc4W/O5RjYjfGyVt8OpHgbDarHKqpkvExaxZ0hLCIikuqi9U6xNaUhKGcvBsAt6QDW HCq5xmNZei2qptwmL+il2m+eGmxkkmQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-25-a1ZuldThM6K-oEP41xpdpQ-1; Tue, 10 Aug 2021 23:06:51 -0400 X-MC-Unique: a1ZuldThM6K-oEP41xpdpQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 74FF6DC22; Wed, 11 Aug 2021 03:06:49 +0000 (UTC) Received: from llong.com (unknown [10.22.17.215]) by smtp.corp.redhat.com (Postfix) with ESMTP id 78AEF5D6CF; Wed, 11 Aug 2021 03:06:47 +0000 (UTC) From: Waiman Long To: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli , Frederic Weisbecker , Marcelo Tosatti , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Waiman Long Subject: [PATCH v4 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Date: Tue, 10 Aug 2021 23:06:06 -0400 Message-Id: <20210811030607.13824-6-longman@redhat.com> In-Reply-To: <20210811030607.13824-1-longman@redhat.com> References: <20210811030607.13824-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Update Documentation/admin-guide/cgroup-v2.rst on the newly introduced "isolated" cpuset partition type as well as the ability to create non-top cpuset partition with no cpu allocated to it. Signed-off-by: Waiman Long --- Documentation/admin-guide/cgroup-v2.rst | 104 +++++++++++++++--------- 1 file changed, 64 insertions(+), 40 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 5c7377b5bd3e..a8faaba1950e 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2080,8 +2080,9 @@ Cpuset Interface Files It accepts only the following input values when written to. ======== ================================ - "root" a partition root - "member" a non-root member of a partition + "member" Non-root member of a partition + "root" Partition root + "isolated" Partition root without load balancing ======== ================================ When set to be a partition root, the current cgroup is the @@ -2090,9 +2091,14 @@ Cpuset Interface Files partition roots themselves and their descendants. The root cgroup is always a partition root. - There are constraints on where a partition root can be set. - It can only be set in a cgroup if all the following conditions - are true. + When set to "isolated", the CPUs in that partition root will + be in an isolated state without any load balancing from the + scheduler. Tasks in such a partition must be explicitly bound + to each individual CPU. + + There are constraints on where a partition root can be set + ("root" or "isolated"). 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. @@ -2103,51 +2109,69 @@ Cpuset Interface Files eliminating corner cases that have to be handled if such a condition is allowed. - Setting it to partition root will take the CPUs away from the - effective CPUs of the parent cgroup. Once it is set, this + Setting it to a partition root will take the CPUs away from + the effective CPUs of the parent cgroup. Once it is set, this file cannot be reverted back to "member" 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. + A parent partition may distribute all its CPUs to its child + partitions as long as it is not the root cgroup and there is no + task directly associated with that parent partition. Otherwise, + there must be at least one cpu left in the parent partition. + A new task cannot be moved to a partition root with no effective + cpu. + + Once becoming a partition root, changes to "cpuset.cpus" + is generally allowed as long as the first condition above + (cpu exclusivity rule) is true. + + Sometimes, changes to "cpuset.cpus" or cpu hotplug may cause + the state of the partition root to become invalid when the + other constraints of partition root are violated. Therefore, + it is recommended that users should always set "cpuset.cpus" + to the proper value first before enabling partition. In case + "cpuset.cpus" has to be modified after partition is enabled, + users should check the state of "cpuset.cpus.partition" after + making change to it to make sure that the partition is still + valid. + + On read, the "cpuset.cpus.partition" file can show the following + values. ============== ============================== "member" Non-root member of a partition "root" Partition root + "isolated" Partition root without load balancing "root invalid" Invalid 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 invalid 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 itself. In this - case, it is not a real partition even though the restriction - of the first partition root condition above will still apply. - The cpu affinity of all the tasks in the cgroup will then be - associated with CPUs in the nearest ancestor partition. - - An invalid 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 cpu - affinity of all the tasks in the formerly invalid partition - will be associated to the CPUs of the newly formed partition. - Changing the partition state of an invalid partition root to - "member" is always allowed even if child cpusets are present. + A partition root becomes invalid if all the CPUs requested in + "cpuset.cpus" become unavailable. This can happen if all the + CPUs have been offlined, or the state of an ancestor partition + root become invalid. In this case, it is not a real partition + even though the restriction of the cpu exclusivity rule will + still apply. The cpu affinity of all the tasks in the cgroup + will then be associated with CPUs in the nearest ancestor + partition. + + In the special case of a parent partition competing with a child + partition for the only CPU left, the parent partition wins and + the child partition becomes invalid. + + An invalid partition root can be transitioned back to a real + partition root if at least one of the requested CPUs become + available again. In this case, the cpu affinity of all the tasks + in the formerly invalid partition will be associated to the CPUs + of the newly formed partition. Changing the partition state of + an invalid partition root to "member" is always allowed even if + child cpusets are present. However changing a partition root back + to member will not be allowed if child partitions are present. + + Poll and inotify events are triggered whenever the state + of "cpuset.cpus.partition" changes. That includes changes + caused by write to "cpuset.cpus.partition" and cpu hotplug. + This will allow a user space agent to monitor changes caused + by hotplug events. Device controller -- 2.18.1