From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
Juri Lelli <juri.lelli@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition
Date: Wed, 12 Apr 2023 09:28:21 -1000 [thread overview]
Message-ID: <ZDcGVebCpyktxyWh@slm.duckdns.org> (raw)
In-Reply-To: <20230412153758.3088111-1-longman@redhat.com>
Hello, Waiman.
On Wed, Apr 12, 2023 at 11:37:53AM -0400, Waiman Long wrote:
> This patch series introduces a new "isolcpus" partition type to the
> existing list of {member, root, isolated} types. The primary reason
> of adding this new "isolcpus" partition is to facilitate the
> distribution of isolated CPUs down the cgroup v2 hierarchy.
>
> The other non-member partition types have the limitation that their
> parents have to be valid partitions too. It will be hard to create a
> partition a few layers down the hierarchy.
>
> It is relatively rare to have applications that require creation of
> a separate scheduling domain (root). However, it is more common to
> have applications that require the use of isolated CPUs (isolated),
> e.g. DPDK. One can use the "isolcpus" or "nohz_full" boot command options
> to get that statically. Of course, the "isolated" partition is another
> way to achieve that dynamically.
>
> Modern container orchestration tools like Kubernetes use the cgroup
> hierarchy to manage different containers. If a container needs to use
> isolated CPUs, it is hard to get those with existing set of cpuset
> partition types. With this patch series, a new "isolcpus" partition
> can be created to hold a set of isolated CPUs that can be pull into
> other "isolated" partitions.
>
> The "isolcpus" partition is special that there can have at most one
> instance of this in a system. It serves as a pool for isolated CPUs
> and cannot hold tasks or sub-cpusets underneath it. It is also not
> cpu-exclusive so that the isolated CPUs can be distributed down the
> sibling hierarchies, though those isolated CPUs will not be useable
> until the partition type becomes "isolated".
>
> Once isolated CPUs are needed in a cgroup, the administrator can write
> a list of isolated CPUs into its "cpuset.cpus" and change its partition
> type to "isolated" to pull in those isolated CPUs from the "isolcpus"
> partition and use them in that cgroup. That will make the distribution
> of isolated CPUs to cgroups that need them much easier.
I'm not sure about this. It feels really hacky in that it side-steps the
distribution hierarchy completely. I can imagine a non-isolated cpuset
wanting to allow isolated cpusets downstream but that should be done
hierarchically - e.g. by allowing a cgroup to express what isolated cpus are
allowed in the subtree. Also, can you give more details on the targeted use
cases?
Thanks.
--
tejun
next prev parent reply other threads:[~2023-04-12 19:28 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-12 15:37 [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition Waiman Long
2023-04-12 19:28 ` Tejun Heo [this message]
[not found] ` <1ce6a073-e573-0c32-c3d8-f67f3d389a28@redhat.com>
2023-04-12 20:22 ` Tejun Heo
2023-04-12 20:33 ` Waiman Long
2023-04-13 0:03 ` Tejun Heo
2023-04-13 0:26 ` Waiman Long
2023-04-13 0:33 ` Tejun Heo
2023-04-13 0:55 ` Waiman Long
2023-04-13 1:17 ` Tejun Heo
2023-04-13 1:55 ` Waiman Long
2023-04-14 1:22 ` Waiman Long
2023-04-14 16:54 ` Tejun Heo
2023-04-14 17:29 ` Waiman Long
2023-04-14 17:34 ` Tejun Heo
2023-04-14 17:38 ` Waiman Long
2023-04-14 19:06 ` Waiman Long
2023-05-02 18:01 ` Michal Koutný
2023-05-02 21:26 ` Waiman Long
2023-05-02 22:27 ` Michal Koutný
2023-05-04 3:01 ` Waiman Long
2023-05-05 16:03 ` Tejun Heo
2023-05-05 16:25 ` Waiman Long
2023-05-08 1:03 ` Waiman Long
2023-05-22 19:49 ` Tejun Heo
2023-05-28 21:18 ` Waiman Long
2023-06-05 18:03 ` Tejun Heo
2023-06-05 20:00 ` Waiman Long
2023-06-05 20:27 ` Tejun Heo
2023-06-06 2:47 ` Waiman Long
2023-06-06 19:58 ` Tejun Heo
2023-06-06 20:11 ` Waiman Long
2023-06-06 20:13 ` Tejun Heo
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