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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Message-ID: <3891d05b-3d0d-b41d-7454-0f5e0d749ded@bytedance.com>
Date:   Mon, 12 Jun 2023 10:40:33 +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 2023/6/10 Benjamin Segall wrote:
> Hao Jia <jiahao.os@...edance.com> writes:
> 
>> 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
> 
> Yeah, the obvious fixes are to either add an update_rq_clock in
> rq_attach_root as you suggest, or put it in set_rq_offline instead of
> the callers.

Thanks for your suggestion. I will do it in the next version.

Thanks,
Hao