path: root/init
diff options
authorPaul E. McKenney <>2015-02-19 10:51:32 -0800
committerPaul E. McKenney <>2015-02-26 12:03:03 -0800
commitee42571f4381f184e2672dd34ab411e5bf5bd5e0 (patch)
tree6dc7829e3529fae2f519ab8dc1a665f8109cc311 /init
parent5afff48bdf7481570c9385a8a674a81ffb8f09ee (diff)
rcu: Add Kconfig option to expedite grace periods during boot
This commit adds a CONFIG_RCU_EXPEDITE_BOOT Kconfig parameter that emulates a very early boot rcu_expedite_gp(). A late-boot call to rcu_end_inkernel_boot() will provide the corresponding rcu_unexpedite_gp(). The late-boot call to rcu_end_inkernel_boot() should be made just before init is spawned. According to Arjan: > To show the boot time, I'm using the timestamp of the "Write protecting" > line, that's pretty much the last thing we print prior to ring 3 execution. > > A kernel with default RCU behavior (inside KVM, only virtual devices) > looks like this: > > [ 0.038724] Write protecting the kernel read-only data: 10240k > > a kernel with expedited RCU (using the command line option, so that I > don't have to recompile between measurements and thus am completely > oranges-to-oranges) > > [ 0.031768] Write protecting the kernel read-only data: 10240k > > which, in percentage, is an 18% improvement. Reported-by: Arjan van de Ven <> Signed-off-by: Paul E. McKenney <> Tested-by: Arjan van de Ven <>
Diffstat (limited to 'init')
1 files changed, 13 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index f5dbc6d4261b..9a0592516f48 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -791,6 +791,19 @@ config RCU_NOCB_CPU_ALL
+ bool
+ default n
+ help
+ This option enables expedited grace periods at boot time,
+ as if rcu_expedite_gp() had been invoked early in boot.
+ The corresponding rcu_unexpedite_gp() is invoked from
+ rcu_end_inkernel_boot(), which is intended to be invoked
+ at the end of the kernel-only boot sequence, just before
+ init is exec'ed.
+ Accept the default if unsure.
endmenu # "RCU Subsystem"
config BUILD_BIN2C