linux-kernel - Re: [External] Re: [PATCH v4 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs

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Date:   Fri, 9 Jun 2023 11:19:03 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     Benjamin Segall <bsegall@...gle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v4 4/4] sched/core: Avoid multiple calling
 update_rq_clock() in unthrottle_offline_cfs_rqs()



On 2023/6/9 Benjamin Segall wrote:
> Hao Jia <jiahao.os@...edance.com> writes:
> 
>> This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
>> ------------[ cut here ]------------
>> rq->clock_update_flags & RQCF_UPDATED
>> WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
>> update_rq_clock+0xaf/0x180
>> Call Trace:
>>   <TASK>
>>   unthrottle_cfs_rq+0x4b/0x300
>>   rq_offline_fair+0x89/0x90
>>   set_rq_offline.part.118+0x28/0x60
>>   rq_attach_root+0xc4/0xd0
>>   cpu_attach_domain+0x3dc/0x7f0
>>   partition_sched_domains_locked+0x2a5/0x3c0
>>   rebuild_sched_domains_locked+0x477/0x830
>>   rebuild_sched_domains+0x1b/0x30
>>   cpuset_hotplug_workfn+0x2ca/0xc90
>>   ? balance_push+0x56/0xf0
>>   ? _raw_spin_unlock+0x15/0x30
>>   ? finish_task_switch+0x98/0x2f0
>>   ? __switch_to+0x291/0x410
>>   ? __schedule+0x65e/0x1310
>>   process_one_work+0x1bc/0x3d0
>>   worker_thread+0x4c/0x380
>>   ? preempt_count_add+0x92/0xa0
>>   ? rescuer_thread+0x310/0x310
>>   kthread+0xe6/0x110
>>   ? kthread_complete_and_exit+0x20/0x20
>>   ret_from_fork+0x1f/0x30
>>
>> The rq clock has been updated before the set_rq_offline()
>> function runs, so we don't need to call update_rq_clock() in
>> unthrottle_offline_cfs_rqs().
> 
> I don't think we do in the path from rq_attach_root (though that's easy
> enough to fix, of course).
> 

Thanks for your review.

Now our fix method is that after applying patch1, we update the rq clock 
before set_rq_offline(). Then use rq_clock_{start, stop}_loop_update to 
avoid updating the rq clock multiple times in unthrottle_cfs_rq().

Do you have any better suggestions?

Thanks,
Hao