linux-kernel - Re: [PATCH] rcu/nocb: Add an option to ON/OFF an offloading from RT context

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Date:   Tue, 10 May 2022 10:14:56 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraj.iitr10@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH] rcu/nocb: Add an option to ON/OFF an offloading from RT
 context

On Tue, May 10, 2022 at 04:07:23PM +0200, Sebastian Andrzej Siewior wrote:
> On 2022-05-05 12:09:15 [-0700], Paul E. McKenney wrote:
> > All good points!
> > 
> > Some questions and comments below.
> > 
> > Adding Sebastian on CC for his perspective.
> 
> Thank you.
> I may missing things, I tried to digest the thread…
> 
> In my understanding: The boosting option is used to allow a SCHED_OTHER
> task within a RCU section to allow to leave the RCU section while tasks
> with higher priority occupy the CPU.
> As far as the RCU callbacks are concerned, I'm not aware that it would
> be beneficial to run them with an elevated priority. On SMP systems,
> there is the suggestion to have a housekeeping CPU and to offload the
> RCU callbacks to this CPU and no to bother the CPU with the RT workload.

Agreed, even within RT, there are multiple ways to get this job done.

							Thanx, Paul