linux-kernel - [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu

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Date:   Thu, 1 Sep 2022 21:14:36 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...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>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v6 2/2] rcu: Offload callback processing from all CPUs in the absence of rcu_nocbs=

Offload callback processing from all CPUs as long as there is no
"rcu_nocbs=" boot parameter. This also means: whether
CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y takes effect does not depend on
the absence of "nohz_full=".

Suggested-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 kernel/rcu/Kconfig     | 4 ++--
 kernel/rcu/tree_nocb.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index d471d22a5e21b43..35b94f5f6767f00 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -270,8 +270,8 @@ config RCU_NOCB_CPU_DEFAULT_ALL
 	default n
 	help
 	  Use this option to offload callback processing from all CPUs
-	  by default, in the absence of the rcu_nocbs or nohz_full boot
-	  parameter. This also avoids the need to use any boot parameters
+	  by default, in the absence of the rcu_nocbs boot parameter.
+	  This also avoids the need to use any boot parameters
 	  to achieve the effect of offloading all CPUs on boot.
 
 	  Say Y here if you want offload all CPUs by default on boot.
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 8b6dceeabde0b4d..cfbdd78d6c33158 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1219,7 +1219,7 @@ void __init rcu_init_nohz(void)
 #endif
 
 #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
-	if (!rcu_state.nocb_is_setup && !cpumask)
+	if (!rcu_state.nocb_is_setup)
 		cpumask = cpu_possible_mask;
 #endif
 
-- 
2.25.1