From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Date: Fri, 27 Aug 2021 21:14:01 -0400 Message-ID: References: <20210825213750.6933-1-longman@redhat.com> <20210825213750.6933-6-longman@redhat.com> <32e27fcc-32f1-b26c-ae91-9e03f7e433af@redhat.com> <392c3724-f583-c7fc-cfa1-a3f1665114c9@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1630113246; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nj7lN9b3OW9PxFPw9p3QaG1rQrZn9spoM1KJO1HMw1U=; b=A4dzNDypRsANDa1pVg1DfcJKC3AeuzVqI/F2sN9U5WyLrRgudYokmWn6/FKp29JdUtpDNU OGw349B1vwMuvYMNMev+arKbHt1fAAgPZ1aRSdSemGsBd0tfpZTPP4W2ECt8avwlCJKjgq ekctGLWwbBEl2uru6xbRluuaPsqoHzE= In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Tejun Heo , Waiman Long Cc: Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli , Frederic Weisbecker , Marcelo Tosatti , =?UTF-8?Q?Michal_Koutn=c3=bd?= On 8/27/21 7:35 PM, Tejun Heo wrote: > Hello, > > On Fri, Aug 27, 2021 at 06:50:10PM -0400, Waiman Long wrote: >> The cpu exclusivity rule is due to the setting of CPU_EXCLUSIVE bit. This is >> a pre-existing condition unless you want to change how the >> cpuset.cpu_exclusive works. >> >> So the new rules will be: >> >> 1) The "cpuset.cpus" is not empty and the list of CPUs are exclusive. > Empty cpu list can be considered an exclusive one. It doesn't make sense to me to have a partition with no cpu configured at all. I very much prefer the users to set cpuset.cpus first before turning it into a partition. > >> 2) The parent cgroup is a partition root (can be an invalid one). > Does this mean a partition parent can't stop being a partition if one or > more of its children become partitions? If so, it violates the rule that a > descendant shouldn't be able to restrict what its ancestors can do. No. As I said in the documentation, transitioning from partition root to member is allowed. Against, it is illogical to allow a cpuset to become a potential partition if it parent is not even a partition root at all. In the case that the parent is reverted back to a member, the child partitions will stay invalid forever unless the parent become a valid partition again. > >> 3) The "cpuset.cpus" is a subset of the parent's cpuset.cpus.allowed. > Why not just go by effective? This would mean that a parent can't withdraw > CPUs from its allowed set once descendants are configured. Restrictions like > this are fine when the entire hierarchy is configured by a single entity but > become awkward when configurations are multi-tiered, automated and dynamic. The original rule is to be based on effective cpus. However, to properly handle the case of allowing offlined cpus to be included in the partition, I have to change it to cpu_allowed instead. I can certainly change it back to effective if you prefer. > >> 4) No child cgroup with cpuset enabled. > idk, maybe? I'm having a hard time seeing the point in adding these > restrictions when the state transitions are asynchronous anyway. Would it > help if we try to separate what's absoluately and technically necessary and > what seems reasonable or high bar and try to justify why each of the latter > should be added? This rule is there mainly for ease of implementation. Otherwise, I need to add additional code to handle the conversion of child cpusets which can be rather complex and require a lot more debugging. This rule will no longer apply once the cpuset becomes a partition root. Cheers, Longman