linux-kernel - Re: [PATCH-cgroup 3/4] cgroup/cpuset: Keep track of CPUs in isolated partitions

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Date:   Wed, 18 Oct 2023 14:24:00 -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 3/4] cgroup/cpuset: Keep track of CPUs in isolated
 partitions

On 10/18/23 14:08, Tejun Heo wrote:
> On Wed, Oct 18, 2023 at 09:30:04AM -0400, Waiman Long wrote:
>> On 10/18/23 05:26, Tejun Heo wrote:
>>> On Fri, Oct 13, 2023 at 02:11:21PM -0400, Waiman Long wrote:
>>> ...
>>>> @@ -3875,6 +3931,13 @@ static struct cftype dfl_files[] = {
>>>>    		.flags = CFTYPE_ONLY_ON_ROOT | CFTYPE_DEBUG,
>>>>    	},
>>>> +	{
>>>> +		.name = "cpus.isolated",
>>>> +		.seq_show = cpuset_common_seq_show,
>>>> +		.private = FILE_ISOLATED_CPULIST,
>>>> +		.flags = CFTYPE_ONLY_ON_ROOT | CFTYPE_DEBUG,
>>>> +	},
>>> I'd much rather show this in a wq sysfs file along with other related masks,
>>> and not in a DEBUG file.
>> It can certainly be exposed as a permanent addition to the cgroup control
>> files instead of a debug only file. However this set of isolated CPUs may be
>> used by others not just by workqueue. So I doubt if it should be a sysfs
>> file in the workqueue directory. I can see if it is possible to put a
>> symlink there point back to the cgroupfs.
> I don't know whether it will happen but let's say there will be three
> subsystems which call into workqueue for this. Wouldn't it be better to have
> all of them in workqueue sysfs using a consistent naming scheme? What does
> putting it in cgroupfs buy us?

If you mean saving the exclusion cpumask no matter who the caller is, we 
can add another exclusion cpumask to save it and expose it to sysfs. 
This should be done in the first workqueue patch, not as part of this 
patch. I expose this isolated cpumask for testing purpose to be checked 
by the test_cpuset_prs.sh script for correctness. As said, I can expose 
it without cgroup_debug if you think the information is useful in general.

Cheers,
Longman