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

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Message-ID: <ZTc57JX2qZiXn3p4@mtj.duckdns.org>
Date:   Mon, 23 Oct 2023 17:28:44 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH-cgroup 1/4] workqueue: Add
 workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask

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