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: <25bebe6f-9ff4-ed75-0041-2c6207c7d6f9@redhat.com>
Date:   Wed, 25 Oct 2023 14:47:00 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
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


On 10/23/23 23:28, Tejun Heo wrote:
> 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.

I have implemented the fallback to the user requested cpumask in the 
failure case.

Cheers,
Longman