linux-kernel - Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting after every update

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Message-ID: <398c710f-2e4e-4b35-a8a3-4c8d64f2fe68@redhat.com>
Date: Mon, 10 Mar 2025 15:18:54 -0400
From: Waiman Long <llong@...hat.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>,
 Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Qais Yousef <qyousef@...alina.io>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Swapnil Sapkal <swapnil.sapkal@....com>,
 Shrikanth Hegde <sshegde@...ux.ibm.com>, Phil Auld <pauld@...hat.com>,
 luca.abeni@...tannapisa.it, tommaso.cucinotta@...tannapisa.it,
 Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting
 after every update


On 3/10/25 2:54 PM, Dietmar Eggemann wrote:
> On 10/03/2025 10:37, Juri Lelli wrote:
>> Rebuilding of root domains accounting information (total_bw) is
>> currently broken on some cases, e.g. suspend/resume on aarch64. Problem
> Nit: Couldn't spot any arch dependency here. I guess it was just tested
> on Arm64 platforms so far.
>
> [...]
>
>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>> index 44093339761c..363ad268a25b 100644
>> --- a/kernel/sched/topology.c
>> +++ b/kernel/sched/topology.c
>> @@ -2791,6 +2791,7 @@ void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new[],
>>   	ndoms_cur = ndoms_new;
>>   
>>   	update_sched_domain_debugfs();
>> +	dl_rebuild_rd_accounting();
> Won't dl_rebuild_rd_accounting()'s lockdep_assert_held(&cpuset_mutex)
> barf when called via cpuhp's:
>
> sched_cpu_deactivate()
>
>    cpuset_cpu_inactive()
>
>      partition_sched_domains()
>
>        partition_sched_domains_locked()
>
>          dl_rebuild_rd_accounting()
>
> ?
>
> [...]

Right. If cpuhp_tasks_frozen is true, partition_sched_domains() will be 
called without holding cpuset mutex.

Well, I think we will need an additional wrapper in cpuset.c that 
acquires the cpuset_mutex first before calling partition_sched_domains() 
and use the new wrapper in these cases.

Cheers,
Longman