Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Mon, 11 Apr 2022 15:49:06 +0200
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@kernel.org>, rcu@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH RFC] rcu/nocb: Provide default all-CPUs mask for
 RCU_NOCB_CPU=y
Message-ID: <YlQx0rZzrdWIA5w+@pc638.lan>
References: <20220407210734.2548973-1-joel@joelfernandes.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220407210734.2548973-1-joel@joelfernandes.org>
Precedence: bulk

Hello, Joel.

> On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided
> which ends up not offloading any CPU. This patch removes yet another
> dependency from the bootloader having to know about RCU, about how many
> CPUs the system has, and about how to provide the mask. Basically, I
> think we should stop pretending that the user knows what they are doing :).
> In other words, if NO_CB_CPU is enabled, lets make use of it.
> 
Could you also please modify the documentation accordingly and send v2?

<snip>
urezki@pc638:~/data/raid0/coding/linux-rcu.git$ grep -rn RCU_NOCB_CPU ./Documentation/
./Documentation/timers/no_hz.rst:188:using the CONFIG_RCU_NOCB_CPU=y Kconfig option.  The specific CPUs to
./Documentation/admin-guide/kernel-parameters.txt:4380:                 In kernels built with CONFIG_RCU_NOCB_CPU=y,
./Documentation/admin-guide/kernel-parameters.txt:4507:                 When RCU_NOCB_CPU is set, also adjust the
./Documentation/admin-guide/kernel-per-CPU-kthreads.rst:311:3.  Build with CONFIG_RCU_NOCB_CPU=y and boot with the rcu_nocbs=
./Documentation/admin-guide/kernel-per-CPU-kthreads.rst:331:2.  Build with CONFIG_RCU_NOCB_CPU=n, which will prevent these
./Documentation/RCU/Design/Requirements/Requirements.rst:1424:``CONFIG_RCU_NOCB_CPU=y`` and booted with ``rcu_nocbs=1-63``, where
urezki@pc638:~/data/raid0/coding/linux-rcu.git$ grep -rn RCU_NOCB_CPU ./kernel/rcu/
...
./kernel/rcu/Kconfig:198:config RCU_NOCB_CPU
..
<snip>

--
Uladzislau Rezki