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) <qyousef@xxxxxxxxxxx>
---
Changes since v1:
* Use module_param() instead of module_param_cb()
* Add new CONFIG_RCU_LAZY_DEFAULT_OFF to force default off.
* Remove unnecessary READ_ONCE()
Tested on qemu only this time with various config/boot configuration to ensure
expected values are in sysfs.
Did a bunch of build tests against various configs/archs.
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 65731b060e3f..2f0386a12aa7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5021,6 +5021,11 @@
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 bdd7eadb33d8..e7d2dd267593 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 3ac3c846105f..8b7675624815 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2719,6 +2719,9 @@ __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
@@ -2744,6 +2747,8 @@ 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
/**
@@ -2792,7 +2797,7 @@ 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);
--
2.34.1
