linux-kernel - Re: [PATCH 5/6] cgroup/cpuset: Free DL BW in case can

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Date:   Wed, 29 Mar 2023 18:39:23 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Waiman Long <longman@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        luca.abeni@...tannapisa.it, claudio@...dence.eu.com,
        tommaso.cucinotta@...tannapisa.it, bristot@...hat.com,
        mathieu.poirier@...aro.org, cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 5/6] cgroup/cpuset: Free DL BW in case can_attach() fails

On 29/03/2023 16:31, Waiman Long wrote:
> On 3/29/23 10:25, Waiman Long wrote:
>>
>> On 3/29/23 08:55, Juri Lelli wrote:
>>> From: Dietmar Eggemann <dietmar.eggemann@....com>

[...]

>>> @@ -2518,11 +2547,21 @@ static int cpuset_can_attach(struct
>>> cgroup_taskset *tset)
>>>   static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>>>   {
>>>       struct cgroup_subsys_state *css;
>>> +    struct cpuset *cs;
>>>         cgroup_taskset_first(tset, &css);
>>> +    cs = css_cs(css);
>>>         mutex_lock(&cpuset_mutex);
>>> -    css_cs(css)->attach_in_progress--;
>>> +    cs->attach_in_progress--;
>>> +
>>> +    if (cs->nr_migrate_dl_tasks) {
>>> +        int cpu = cpumask_any(cs->effective_cpus);
>>> +
>>> +        dl_bw_free(cpu, cs->sum_migrate_dl_bw);
>>> +        reset_migrate_dl_data(cs);
>>> +    }
>>> +
> 
> Another nit that I have is that you may have to record also the cpu
> where the DL bandwidth is allocated in cpuset_can_attach() and free the
> bandwidth back into that cpu or there can be an underflow if another cpu
> is chosen.

Many thanks for the review!

But isn't the DL BW control `struct dl_bw` per `struct root_domain`
which is per exclusive cpuset. So as long cpu is from
`cs->effective_cpus` shouldn't this be fine?