From: Ran Wang <ran.wang_1@nxp.com>
To: "Rafael J . Wysocki" <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Jiafei Pan <jiafei.pan@nxp.com>,
"linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Sebastian Siewior <bigeasy@linutronix.de>,
Viresh Kumar <viresh.kumar@linaro.org>
Subject: RE: [PATCH] rt: cpufreq: Fix cpu hotplug hang
Date: Tue, 23 Feb 2021 02:26:02 +0000 [thread overview]
Message-ID: <AM6PR04MB5413DB3654A87D50C909004CF1809@AM6PR04MB5413.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20210222140107.qk2ymlwyyxspluge@linutronix.de>
Hello Rafael,
On Monday, February 22, 2021 10:01 PM, Sebastian Siewior wrote:
>
> On 2021-02-19 16:44:20 [+0800], Ran Wang wrote:
> > When selecting PREEMPT_RT, cpufreq_driver->stop_cpu(policy) might got
> > stuck due to irq_work_sync() pending for work on lazy_list. That’s
> > because lazy_list may have no chance to be served in softirq context
> > sometimes. Below is one of scenarios that was captured:
> >
> > ...
> > ret_from_fork
> > kthread
> > smpboot_thread_fn
> > cpuhp_thread_fun
> > cpuhp_invoke_callback: state: 193
> > cpuhp_cpufreq_online
> > cpufreq_online
> > cpufreq_driver->stop_cpu(policy);
> > cpufreq_dbs_governor_stop
> > sugov_stop // kernel/sched/cpufreq_schedutil.c
> > irq_work_sync(&sg_policy->irq_work);
> >
> > This is observed on LX2160ARDB (16 A72 cores) with cpufreq governor of
> > ‘schedutil’ or ‘ondemand’.
>
> While staring at it, why do we invoke schedule_work_on() and
> kthread_queue_work() from inside irq_work() instead invoking it directly? It raises an interrupt in which it kicks a user thread.
> Couldn't we do it without irq_work?
Could you please help comment on above question (I just follow CPU Freq scaling framework, can't tell why) Thank you very much.
Regards,
Ran
next prev parent reply other threads:[~2021-02-23 2:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 8:44 [PATCH] rt: cpufreq: Fix cpu hotplug hang Ran Wang
2021-02-22 14:01 ` Sebastian Siewior
2021-02-23 2:26 ` Ran Wang [this message]
2021-02-23 3:13 ` Viresh Kumar
2021-02-24 16:37 ` Sebastian Siewior
2021-02-25 2:31 ` Ran Wang
2021-03-23 7:00 ` Ran Wang
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