Message-ID: <8787b5f7-9822-e49b-0357-d0ce224ca920@redhat.com>
Date:   Thu, 2 Feb 2023 16:05:14 -0500
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.0
Subject: Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter
 offline CPUs
Content-Language: en-US
From:   Waiman Long <longman@redhat.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        kernel-team@android.com, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org
References: <20230131221719.3176-1-will@kernel.org>
 <20230131221719.3176-2-will@kernel.org>
 <6b068916-5e1b-a943-1aad-554964d8b746@redhat.com>
 <Y9t1sP/6nFht7RSN@hirez.programming.kicks-ass.net>
 <d630ca53-71f0-c735-fbc3-e826479aa86b@redhat.com>
 <Y9wSC1Wxlm8CKKlN@hirez.programming.kicks-ass.net>
 <2bc730db-704d-080b-6869-02f6d0035fad@redhat.com>
 <Y9whrU4IUeleqdrt@slm.duckdns.org>
 <75de91db-d3bc-0c0e-6199-ef00591e8878@redhat.com>
In-Reply-To: <75de91db-d3bc-0c0e-6199-ef00591e8878@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2/2/23 15:53, Waiman Long wrote:
>
> On 2/2/23 15:48, Tejun Heo wrote:
>> On Thu, Feb 02, 2023 at 03:46:02PM -0500, Waiman Long wrote:
>>>>> I will work on a patchset to do that as a counter offer.
>>>> We will need a small and simple patch for /urgent, or I will need to
>>>> revert all your patches -- your call.
>>>>
>>>> I also don't tihnk you fully appreciate the ramifications of
>>>> task_cpu_possible_mask(), cpuset currently gets that quite wrong.
>>> OK, I don't realize the urgency of that. If it is that urgent, I 
>>> will have
>>> no objection to get it in for now. We can improve it later on. So 
>>> are you
>>> planning to get it into the current 6.2 rc or 6.3?
>>>
>>> Tejun, are you OK with that as you are the cgroup maintainer?
>> Yeah, gotta fix the regression but is there currently a solution 
>> which fixes
>> the regression but doesn't further break other stuff?
>
> I believe there is a better way to do that, but it will need more time 
> to flex out. Since cpuset_cpus_allowed() is only used by 
> kernel/sched/core.c, Peter will be responsible if it somehow breaks 
> other stuff.

Maybe my cpuset patch that don't update task's cpumask on cpu offline 
event can help. However, I don't know the exact scenario where the 
regression happen, so it may not.

Cheers,
Longman