From fb1f6554559da0f00b98a4dd5fe8ca2b67d364fc Mon Sep 17 00:00:00 2001 From: Qais Yousef Date: Sun, 3 Dec 2023 01:12:52 +0000 Subject: [PATCH] rcu: Provide a boot time parameter to control lazy RCU mainline inclusion from mainline-v6.9-rc1 category: performance To allow more flexible arrangements while still provide a single kernel for distros, provide a boot time parameter to enable/disable lazy RCU. Specify: rcutree.enable_rcu_lazy=[y|1|n|0] Which also requires rcu_nocbs=all at boot time to enable/disable lazy RCU. To disable it by default at build time when CONFIG_RCU_LAZY=y, the new CONFIG_RCU_LAZY_DEFAULT_OFF can be used. Signed-off-by: Qais Yousef (Google) Tested-by: Andrea Righi Reviewed-by: Paul E. McKenney Signed-off-by: Boqun Feng (cherry picked from commit 7f66f099de4dc4b1a66a3f94e6db16409924a6f8) Signed-off-by: Wentao Guan --- Documentation/admin-guide/kernel-parameters.txt | 5 +++++ kernel/rcu/Kconfig | 13 +++++++++++++ kernel/rcu/tree.c | 7 ++++++- 3 files changed, 24 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9ce75836fc73c..c02213d34676f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4983,6 +4983,11 @@ this kernel boot parameter, forcibly setting it to zero. + rcutree.enable_rcu_lazy= [KNL] + To save power, batch RCU callbacks and flush after + delay, memory pressure or callback list growing too + big. + rcuscale.gp_async= [KNL] Measure performance of asynchronous grace-period primitives such as call_rcu(). diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index bdd7eadb33d8f..e7d2dd2675931 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -314,6 +314,19 @@ config RCU_LAZY To save power, batch RCU callbacks and flush after delay, memory pressure, or callback list growing too big. + Requires rcu_nocbs=all to be set. + + Use rcutree.enable_rcu_lazy=0 to turn it off at boot time. + +config RCU_LAZY_DEFAULT_OFF + bool "Turn RCU lazy invocation off by default" + depends on RCU_LAZY + default n + help + Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default + off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch + it back on. + config RCU_DOUBLE_CHECK_CB_TIME bool "RCU callback-batch backup time check" depends on RCU_EXPERT diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5684ce5815b33..f25d07ca3ca5c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2753,6 +2753,9 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in) } #ifdef CONFIG_RCU_LAZY +static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF); +module_param(enable_rcu_lazy, bool, 0444); + /** * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and * flush all lazy callbacks (including the new one) to the main ->cblist while @@ -2778,6 +2781,8 @@ void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) __call_rcu_common(head, func, false); } EXPORT_SYMBOL_GPL(call_rcu_hurry); +#else +#define enable_rcu_lazy false #endif /** @@ -2826,7 +2831,7 @@ EXPORT_SYMBOL_GPL(call_rcu_hurry); */ void call_rcu(struct rcu_head *head, rcu_callback_t func) { - __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY)); + __call_rcu_common(head, func, enable_rcu_lazy); } EXPORT_SYMBOL_GPL(call_rcu);