diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-02-19 19:51:32 +0100 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-02-26 21:03:03 +0100 |
| commit | ee42571f4381f184e2672dd34ab411e5bf5bd5e0 (patch) | |
| tree | 6dc7829e3529fae2f519ab8dc1a665f8109cc311 | |
| parent | rcu: Update from rcu_expedited variable to rcu_gp_is_expedited() (diff) | |
| download | linux-ee42571f4381f184e2672dd34ab411e5bf5bd5e0.tar.xz linux-ee42571f4381f184e2672dd34ab411e5bf5bd5e0.zip | |
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 <arjan@linux.intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Arjan van de Ven <arjan@linux.intel.com>
| -rw-r--r-- | include/linux/rcupdate.h | 1 | ||||
| -rw-r--r-- | init/Kconfig | 13 | ||||
| -rw-r--r-- | kernel/rcu/update.c | 11 |
3 files changed, 24 insertions, 1 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 57a4d1f73a00..b9f039b11d31 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -278,6 +278,7 @@ static inline int rcu_preempt_depth(void) /* Internal to kernel */ void rcu_init(void); +void rcu_end_inkernel_boot(void); void rcu_sched_qs(void); void rcu_bh_qs(void); void rcu_check_callbacks(int user); 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 endchoice +config RCU_EXPEDITE_BOOT + 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 diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 5f850823c187..7b12466f90bc 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -64,7 +64,8 @@ module_param(rcu_expedited, int, 0); #ifndef CONFIG_TINY_RCU -static atomic_t rcu_expedited_nesting; +static atomic_t rcu_expedited_nesting = + ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0); /* * Should normal grace-period primitives be expedited? Intended for @@ -109,6 +110,14 @@ EXPORT_SYMBOL_GPL(rcu_unexpedite_gp); #endif /* #ifndef CONFIG_TINY_RCU */ +/* + * Inform RCU of the end of the in-kernel boot sequence. + */ +void rcu_end_inkernel_boot(void) +{ + if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT)) + rcu_unexpedite_gp(); +} #ifdef CONFIG_PREEMPT_RCU |