linux-kernel - Re: [PATCH 0/5] handle kthread_prio kernel cmdline parameter consistently

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Message-ID: <20220112010302.GL947480@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 11 Jan 2022 17:03:02 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Alison Chaiken <achaiken@...ora.tech>
Cc:     tglx@...utronix.de, peterz@...radead.org,
        valentin.schneider@....com, frederic@...nel.org,
        linux-kernel@...r.kernel.org, glenn@...ora.tech,
        alison@...-devel.com
Subject: Re: [PATCH 0/5] handle kthread_prio kernel cmdline parameter
 consistently

On Tue, Jan 11, 2022 at 03:32:49PM -0800, Alison Chaiken wrote:
> When CONFIG_PREEMPT_RT=y, RCU_SOFTIRQ work is moved to dedicated rcuc
> per-core threads.  The rcutree.kthread_prio kernel cmdline parameter
> controls the priority of those threads.
> 
> A provided kthread_prio kernel cmdline parameter also elevates the
> priority of rcuog threads, but only if they are launched from
> rcu_spawn_gp_kthread(), not if they are launched from
> rcu_spawn_one_nocb_kthread().  Fix this inconsistency.
> 
> When CONFIG_RCU_NOCB_CPU=y, an rcu_nocbs command-line parameter
> offloads the work of rcuc on designated cores to new rcuop threads
> that are not pinned to the cores whose expired grace-period timer
> callbacks they run.  While rcuop threads have the same function as
> rcuc threads, their priority is not controlled by the kthread_prio
> parameter.  Add this feature and update the documentation accordingly.
> 
> Alison Chaiken (4):
>   RCU: move kthread_prio bounds-check to a separate function
>   RCU: make priority of grace-period thread consistent
>   RCU: elevate priority of offloaded callback threads
>   RCU: update documentation regarding kthread_prio cmdline parameter

I have queued these for review and testing, thank you!

2/4 appears to have been produced against a pre-merge-window mainline,
so I had to adjust it a bit to queue it on -rcu.  Please check to make
sure that I did not mess anything up.

							Thanx, Paul