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Subject: Re: [PATCH v8 4/6] cpuset: Make generate_sched_domains() recognize
 isolated_cpus
From:   Waiman Long <longman@redhat.com>
To:     Juri Lelli <juri.lelli@redhat.com>
Cc:     Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        kernel-team@fb.com, pjt@google.com, luto@amacapital.net,
        Mike Galbraith <efault@gmx.de>, torvalds@linux-foundation.org,
        Roman Gushchin <guro@fb.com>
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Organization: Red Hat
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Date:   Mon, 28 May 2018 21:24:19 -0400
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On 05/28/2018 09:12 PM, Waiman Long wrote:
> On 05/24/2018 06:28 AM, Juri Lelli wrote:
>> On 17/05/18 16:55, Waiman Long wrote:
>>
>> [...]
>>
>>> @@ -849,7 +860,12 @@ static void rebuild_sched_domains_locked(void)
>>>  	 * passing doms with offlined cpu to partition_sched_domains().
>>>  	 * Anyways, hotplug work item will rebuild sched domains.
>>>  	 */
>>> -	if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
>>> +	if (!top_cpuset.isolation_count &&
>>> +	    !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
>>> +		goto out;
>>> +
>>> +	if (top_cpuset.isolation_count &&
>>> +	   !cpumask_subset(top_cpuset.effective_cpus, cpu_active_mask))
>>>  		goto out;
>> Do we cover the case in which hotplug removed one of the isolated cpus
>> from cpu_active_mask?
> Yes, you are right. That is the remnant of my original patch that allows
> only one isolated_cpus at root. Thanks for spotting that.

I am sorry. I would like to take it back my previous comment. The code
above looks for inconsistency in the state of the effective_cpus mask to
find out if it is racing with a hotplug event. If it is, we can skip the
domain generation as the hotplug event will do that too. The checks are
still valid with the current patchset. So I don't think we need to make
any change here.

Cheers,
Longman