linux-kernel - Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER

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Date:   Sat, 16 Jan 2021 16:13:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, Qian Cai <cai@...hat.com>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Dexuan Cui <decui@...rosoft.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU

On Sat, Jan 16, 2021 at 01:45:23PM +0100, Peter Zijlstra wrote:
> On Sat, Jan 16, 2021 at 02:27:09PM +0800, Lai Jiangshan wrote:

> > I feel nervous to use kthread_park() here and kthread_parkme() in
> > worker thread.  And adding kthread_should_park() to the fast path
> > also daunt me.
> 
> Is that really such a hot path that an additional load is problematic?

I think we can remove it. It would mean the kthread_park() from the
online callback will take a bit longer, as it will have to wait for all
the works to complete, but that should not be a fundamental problem.