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

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Message-ID: <20220914104634.GC1936@lothringen>
Date:   Wed, 14 Sep 2022 12:46:34 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        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 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!