Re: [PATCH-cgroup 1/4] workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask

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>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Shuah Khan <shuah@kernel.org>,
	cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH-cgroup 1/4] workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask
Date: Mon, 23 Oct 2023 17:28:44 -1000	[thread overview]
Message-ID: <ZTc57JX2qZiXn3p4@mtj.duckdns.org> (raw)
In-Reply-To: <f8796057-e7f0-b589-783f-d11538aaafbf@redhat.com>

Hello,

On Wed, Oct 18, 2023 at 03:18:52PM -0400, Waiman Long wrote:
> I have a second thought after taking a further look at that. First of all,
> cpuset_allowed_mask isn't relevant here and the mask can certainly contain
> offline CPUs. So cpu_possible_mask is the proper fallback.
> 
> With the current patch, wq_user_unbound_cpumask is set up initially as 
> (HK_TYPE_WQ ∩ HK_TYPE_DOMAIN) house keeping mask and rewritten by any
> subsequent write to workqueue/cpumask sysfs file. So using

The current behavior is not something which is carefully planned. It's more
accidental than anything. If we can come up with a more intutive and
consistent behavior, that should be fine.

> wq_user_unbound_cpumask has the implied precedence of user-sysfs written
> mask, command line isolcpus or nohz_full option mask and cpu_possible_mask.
> I think just fall back to wq_user_unbound_cpumask if the operation fails
> should be enough.

But yeah, that sounds acceptable.

Thanks.

-- 
tejun