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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Waiman Long <longman@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] cgroup/cpuset: Optimize cpuset_attach() on v2
Date: Wed, 23 Nov 2022 16:19:44 +0100	[thread overview]
Message-ID: <Y346ENzM4+FAjRnn@linutronix.de> (raw)
In-Reply-To: <20221112221939.1272764-3-longman@redhat.com>

On 2022-11-12 17:19:39 [-0500], Waiman Long wrote:
> It was found that with the default hierarchy, enabling cpuset in the
> child cgroups can trigger a cpuset_attach() call in each of the child
> cgroups that have tasks with no change in effective cpus and mems. If
> there are many processes in those child cgroups, it will burn quite a
> lot of cpu cycles iterating all the tasks without doing useful work.

Thank you.

So this preserves the CPU mask upon attaching the cpuset container.

| ~# taskset -pc $$
| pid 1564's current affinity list: 0-2

default mask after boot due to isolcpus=

| ~# echo "+cpu" >> /sys/fs/cgroup/cgroup.subtree_control ; echo "+cpuset" >> /sys/fs/cgroup/cgroup.subtree_control
| ~# taskset -pc $$
| pid 1564's current affinity list: 0-2

okay.

| ~# echo 1-3 > /sys/fs/cgroup/user.slice/cpuset.cpus
| ~# taskset -pc $$
| pid 1564's current affinity list: 1-3

wiped away.

| ~# taskset -pc 2-3 $$ 
| pid 1564's current affinity list: 1-3
| pid 1564's new affinity list: 2,3
| ~# echo 2-4 > /sys/fs/cgroup/user.slice/cpuset.cpus
| ~# taskset -pc 2-3 $$ 
| pid 1564's current affinity list: 2,3
| pid 1564's new affinity list: 2,3

But it works if the mask was changed on purpose.

Sebastian

WARNING: multiple messages have this Message-ID (diff)
From: Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
To: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/2] cgroup/cpuset: Optimize cpuset_attach() on v2
Date: Wed, 23 Nov 2022 16:19:44 +0100	[thread overview]
Message-ID: <Y346ENzM4+FAjRnn@linutronix.de> (raw)
In-Reply-To: <20221112221939.1272764-3-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

On 2022-11-12 17:19:39 [-0500], Waiman Long wrote:
> It was found that with the default hierarchy, enabling cpuset in the
> child cgroups can trigger a cpuset_attach() call in each of the child
> cgroups that have tasks with no change in effective cpus and mems. If
> there are many processes in those child cgroups, it will burn quite a
> lot of cpu cycles iterating all the tasks without doing useful work.

Thank you.

So this preserves the CPU mask upon attaching the cpuset container.

| ~# taskset -pc $$
| pid 1564's current affinity list: 0-2

default mask after boot due to isolcpus=

| ~# echo "+cpu" >> /sys/fs/cgroup/cgroup.subtree_control ; echo "+cpuset" >> /sys/fs/cgroup/cgroup.subtree_control
| ~# taskset -pc $$
| pid 1564's current affinity list: 0-2

okay.

| ~# echo 1-3 > /sys/fs/cgroup/user.slice/cpuset.cpus
| ~# taskset -pc $$
| pid 1564's current affinity list: 1-3

wiped away.

| ~# taskset -pc 2-3 $$ 
| pid 1564's current affinity list: 1-3
| pid 1564's new affinity list: 2,3
| ~# echo 2-4 > /sys/fs/cgroup/user.slice/cpuset.cpus
| ~# taskset -pc 2-3 $$ 
| pid 1564's current affinity list: 2,3
| pid 1564's new affinity list: 2,3

But it works if the mask was changed on purpose.

Sebastian

  parent reply	other threads:[~2022-11-23 15:20 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-12 22:19 [PATCH 0/2] cgroup/cpuset: v2 optimization Waiman Long
2022-11-12 22:19 ` Waiman Long
2022-11-12 22:19 ` [PATCH 1/2] cgroup/cpuset: Skip spread flags update on v2 Waiman Long
2022-11-12 22:19   ` Waiman Long
2022-11-12 22:19 ` [PATCH 2/2] cgroup/cpuset: Optimize cpuset_attach() " Waiman Long
2022-11-12 22:19   ` Waiman Long
2022-11-21 18:50   ` Michal Koutný
2022-11-21 18:50     ` Michal Koutný
2022-11-21 19:11     ` Waiman Long
2022-11-21 19:11       ` Waiman Long
2022-11-23 15:19   ` Sebastian Andrzej Siewior [this message]
2022-11-23 15:19     ` Sebastian Andrzej Siewior
2022-11-14 21:46 ` [PATCH 0/2] cgroup/cpuset: v2 optimization Tejun Heo
2022-11-14 21:46   ` Tejun Heo

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