From 053ca72554df6923d703a1c072f1930e1870b040 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 8 Jan 2025 19:42:42 -0800 Subject: [PATCH] rcu: Add CONFIG_RCU_LAZY delays to call_rcu() kernel-doc header This commit adds a description of the energy-efficiency delays that call_rcu() can impose, along with a pointer to call_rcu_hurry() for latency-sensitive kernel code. Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng --- kernel/rcu/tree.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 2cd193ed854c..780e4b30febb 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3172,6 +3172,13 @@ EXPORT_SYMBOL_GPL(call_rcu_hurry); * * Implementation of these memory-ordering guarantees is described here: * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. + * + * Specific to call_rcu() (as opposed to the other call_rcu*() functions), + * in kernels built with CONFIG_RCU_LAZY=y, call_rcu() might delay for many + * seconds before starting the grace period needed by the corresponding + * callback. This delay can significantly improve energy-efficiency + * on low-utilization battery-powered devices. To avoid this delay, + * in latency-sensitive kernel code, use call_rcu_hurry(). */ void call_rcu(struct rcu_head *head, rcu_callback_t func) {