linux-kernel - Re: [PATCH v2] EXP rcu: Move expedited grace period (GP) work to RT kthread

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Message-ID: <20220408172714.52d64c84@gandalf.local.home>
Date:   Fri, 8 Apr 2022 17:27:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        kernel-team <kernel-team@...roid.com>, Tejun Heo <tj@...nel.org>,
        Tim Murray <timmurray@...gle.com>, Wei Wang <wvw@...gle.com>,
        Kyle Lin <kylelin@...gle.com>,
        Chunwei Lu <chunweilu@...gle.com>,
        Lulu Wang <luluw@...gle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        rcu <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] EXP rcu: Move expedited grace period (GP) work to RT
 kthread_worker

On Fri, 8 Apr 2022 08:58:34 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > I do not see why PREEMPT_RT is special here. Why was it singled out?  
> 
> Because I didn't see the point of doing kthread_create_worker() to create
> a pair of kthread_worker structuress that were never going to be used
> in PREEMPT_RT kernels.
> 
> Or are PREEMPT_RT kernels no longer booting with rcupdate.rcu_normal?
> Last I knew, they all did this to avoid IPI latencies from expedited
> grace periods.  Has this changed?

Honestly, I don't know. But I guess I can go and find out ;-)

-- Steve