From 90d68cedd1d698b5ec8858dfd100e742e9dd6617 Mon Sep 17 00:00:00 2001 From: Qais Yousef Date: Sun, 3 Dec 2023 01:12:52 +0000 Subject: [PATCH] FROMLIST: rcu: Provide a boot time parameter to control lazy RCU 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. Bug: 258241771 Signed-off-by: Qais Yousef (Google) Tested-by: Andrea Righi Signed-off-by: Paul E. McKenney Link: https://lore.kernel.org/lkml/20231203011252.233748-1-qyousef@layalina.io/ [Fix trivial conflicts rejecting newer code that doesn't exist on 6.1] Signed-off-by: Qais Yousef Change-Id: Ib5585ae717a2ba7749f2802101b785c4e5de8a90 --- Documentation/admin-guide/kernel-parameters.txt | 5 +++++ kernel/rcu/Kconfig | 12 ++++++++++++ kernel/rcu/tree.c | 7 ++++++- 3 files changed, 23 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index cba404efdd39..8c2dfe8b36e8 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4882,6 +4882,11 @@ rcu_node tree with an eye towards determining why a new grace period has not yet started. + 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 446e827b079e..5ce3a8c258f3 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -318,6 +318,18 @@ config RCU_LAZY help 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_BOOT_END_DELAY int "Minimum time before RCU may consider in-kernel boot as completed" diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e1d4bde8672e..949c85870a0b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2799,6 +2799,9 @@ __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 @@ -2824,6 +2827,8 @@ void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) return __call_rcu_common(head, func, false); } EXPORT_SYMBOL_GPL(call_rcu_hurry); +#else +#define enable_rcu_lazy false #endif /** @@ -2872,7 +2877,7 @@ EXPORT_SYMBOL_GPL(call_rcu_hurry); */ void call_rcu(struct rcu_head *head, rcu_callback_t func) { - return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY)); + __call_rcu_common(head, func, enable_rcu_lazy); } EXPORT_SYMBOL_GPL(call_rcu);