From patchwork Tue Jul 20 14:18:33 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 12388443 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=-17.2 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 ADD9DC07E9B for ; Tue, 20 Jul 2021 14:27:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 982CC61164 for ; Tue, 20 Jul 2021 14:27:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239856AbhGTNqN (ORCPT ); Tue, 20 Jul 2021 09:46:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:38388 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240059AbhGTNjs (ORCPT ); Tue, 20 Jul 2021 09:39:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626790824; 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=3Bali8rkEps7iXEarLyy6nashKZ29ZfCD2TM56N0zaI=; b=UeqpbPbIEHellL/03s8fftVFyl566k8MIj3razfuOnav/buEEJ55N67ZfeuFh4V9h3UwDh L6lHify7thkhG53LzEj8gvxSPzd74bNHMpUbICV3yrRGv3x03bIQFdsMy/zIFdFampdHaA 9hh8gI0oSd9T+odh8lLh7l5rbb1Mv0A= 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-90-0sglr9-zOWS3UqbaUwzhmg-1; Tue, 20 Jul 2021 10:20:23 -0400 X-MC-Unique: 0sglr9-zOWS3UqbaUwzhmg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1BFEB1084F4C; Tue, 20 Jul 2021 14:20:21 +0000 (UTC) Received: from llong.com (ovpn-116-153.rdu2.redhat.com [10.10.116.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id 586A8369A; Tue, 20 Jul 2021 14:20:19 +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_Koutn=C3=BD?= , Waiman Long Subject: [PATCH v3 8/9] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Date: Tue, 20 Jul 2021 10:18:33 -0400 Message-Id: <20210720141834.10624-9-longman@redhat.com> In-Reply-To: <20210720141834.10624-1-longman@redhat.com> References: <20210720141834.10624-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@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 | 94 +++++++++++++++---------- 1 file changed, 58 insertions(+), 36 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 5c7377b5bd3e..2e101a353ab1 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 +2109,67 @@ 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. + 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. Other constraints for this + operation are as follows. - 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. + 1) Any newly added CPUs must be a subset of the parent's + "cpuset.cpus.effective". + 2) Taking away all the CPUs from the parent's "cpuset.cpus.effective" + is only allowed if there is no task associated with the + parent partition. + 3) Deletion of CPUs that have been distributed to child partition + roots are not allowed. 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. + root to change. 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 when transition to or + from invalid partition root happens. Device controller