linux-kernel - Re: [PATCH] rcu: Provide a boot time parameter to enable lazy RCU

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Date:   Tue, 21 Nov 2023 22:17:52 +0000
From:   Qais Yousef <qyousef@...alina.io>
To:     Andrea Righi <andrea.righi@...onical.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>,
        John Stultz <jstultz@...gle.com>, linux-kernel@...r.kernel.org,
        rcu@...r.kernel.org
Subject: Re: [PATCH] rcu: Provide a boot time parameter to enable lazy RCU

On 11/23/23 07:28, Andrea Righi wrote:
> On Tue, Nov 21, 2023 at 08:53:04PM +0000, Qais Yousef wrote:
> > To allow more flexible opt-in arrangements while still provide a single
> > kernel for distros, provide a boot time parameter to enable lazy RCU.
> > 
> > Specify:
> > 
> > 	rcutree.enable_rcu_lazy
> > 
> > Which also requires
> > 
> > 	rcu_nocbs=all
> > 
> > at boot time to enable lazy RCU assuming CONFIG_RCU_LAZY=y. The
> > parameter will be ignored if CONFIG_RCU_LAZY is not set.
> > 
> > With this change now lazy RCU is disabled by default if the boot
> > parameter is not set even when CONFIG_RCU_LAZY is enabled.
> 
> I'm wondering if we should make this enabled by default if
> CONFIG_RCU_LAZY=y, so we don't break the previous behavior, and those
> who want it disabled (despite having CONFIG_RCU_LAZY=y in their .config)
> can add rcutree.enable_rcu_lazy=0 to the boot options.
> 
> Thanks for working on this!

Sure, thanks for having a look!

Cheers

--
Qais Yousef