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From:   Benjamin Segall <bsegall@google.com>
To:     Hao Jia <jiahao.os@bytedance.com>
Cc:     mingo@redhat.com, peterz@infradead.org, mingo@kernel.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com,
        mgorman@techsingularity.net, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 4/4] sched/core: Avoid multiple calling
 update_rq_clock() in unthrottle_offline_cfs_rqs()
References: <20230613082012.49615-1-jiahao.os@bytedance.com>
        <20230613082012.49615-5-jiahao.os@bytedance.com>
Date:   Tue, 13 Jun 2023 14:52:27 -0700
In-Reply-To: <20230613082012.49615-5-jiahao.os@bytedance.com> (Hao Jia's
        message of "Tue, 13 Jun 2023 16:20:12 +0800")
Message-ID: <xm268rcn9gis.fsf@google.com>
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Hao Jia <jiahao.os@bytedance.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 in the set_rq_offline(),
> so we don't need to call update_rq_clock() in
> unthrottle_offline_cfs_rqs().
> We only need to call rq_clock_start_loop_update() before the
> loop starts and rq_clock_stop_loop_update() after the loop
> to avoid this warning.
>

Both of these cfsb patches look sensible to me.

Reviewed-By: Ben Segall <bsegall@google.com>