Commit 62153417 authored by Qais Yousef's avatar Qais Yousef Committed by Wentao Guan
Browse files

rcu: Provide a boot time parameter to control lazy RCU 

mainline inclusion
from mainline-v6.9-rc1
commit 7f66f099de4dc4b1a66a3f94e6db16409924a6f8
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/IBE3AN



---------------------------

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: default avatarQais Yousef (Google) <qyousef@layalina.io>
Tested-by: default avatarAndrea Righi <andrea.righi@canonical.com>
Reviewed-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
(cherry picked from commit 7f66f099de4dc4b1a66a3f94e6db16409924a6f8)
Signed-off-by: default avatarWentao Guan <guanwentao@uniontech.com>
parent 718d50bf

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -5073,6 +5073,11 @@ 
			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().

kernel/rcu/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/tree.c

+6 −1
Original line number Diff line number Diff line
@@ -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);