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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-02-19 10:51:32 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-02-26 12:03:03 -0800
commitee42571f4381f184e2672dd34ab411e5bf5bd5e0 (patch)
tree6dc7829e3529fae2f519ab8dc1a665f8109cc311 /kernel/rcu/update.c
parent5afff48bdf7481570c9385a8a674a81ffb8f09ee (diff)
downloadlinux-sh-ee42571f4381f184e2672dd34ab411e5bf5bd5e0.tar.gz
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>
Diffstat (limited to 'kernel/rcu/update.c')
-rw-r--r--kernel/rcu/update.c11
1 files changed, 10 insertions, 1 deletions
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