linux-kernel - Re: [PATCH v7 1/1] rcu: Simplify rcu_init

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Date:   Wed, 14 Sep 2022 04:30:06 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/1] rcu: Simplify rcu_init_nohz() cpumask handling

On Wed, Sep 14, 2022 at 12:46:34PM +0200, Frederic Weisbecker wrote:
> On Tue, Sep 13, 2022 at 11:00:36AM +0800, Zhen Lei wrote:
> > In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
> > CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
> > Except that kernels booted without the rcu_nocbs= will not have
> > allocated rcu_nocb_mask.  And the current rcu_init_nohz() function uses
> > its need_rcu_nocb_mask and offload_all local variables to track the
> > rcu_nocb and nohz_full state.
> > 
> > But there is a much simpler approach, namely creating a cpumask pointer
> > to track the default and then using cpumask_available() to check the
> > rcu_nocb_mask state.  This commit takes this approach, thereby simplifying
> > and shortening the rcu_init_nohz() function.
> > 
> > Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> > Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > Acked-by: Frederic Weisbecker <frederic@...nel.org>
> 
> Looks good, thanks!

Queued and pushed, thank you all!

							Thanx, Paul