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rcu: Provide a boot time parameter to control lazy RCU

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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@layalina.io>
Tested-by: Andrea Righi <andrea.righi@canonical.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Qais Yousef 2023-12-03 01:12:52 +00:00 committed by Boqun Feng
parent 499d7e7e83
commit 7f66f099de
3 changed files with 24 additions and 1 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -5034,6 +5034,11 @@
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().

13
kernel/rcu/Kconfig
View File

@ -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

7
kernel/rcu/tree.c
View File

@ -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);