From 2b1d5024e17be459aa6385763ca3faa8f01c52d9 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 11 Jul 2012 20:26:30 +0200 Subject: [PATCH] rcu: Settle config for userspace extended quiescent state Create a new config option under the RCU menu that put CPUs under RCU extended quiescent state (as in dynticks idle mode) when they run in userspace. This require some contribution from architectures to hook into kernel and userspace boundaries. Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Josh Triplett Cc: Kevin Hilman Cc: Max Krasnyansky Cc: Peter Zijlstra Cc: Stephen Hemminger Cc: Steven Rostedt Cc: Sven-Thorsten Dietrich Cc: Thomas Gleixner Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/Kconfig | 10 ++++++++++ include/linux/rcupdate.h | 9 +++++++++ init/Kconfig | 10 ++++++++++ kernel/rcutree.c | 5 ++++- 4 files changed, 33 insertions(+), 1 deletion(-) diff --git a/arch/Kconfig b/arch/Kconfig index 72f2fa189cc5..1401a7587973 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -281,4 +281,14 @@ config SECCOMP_FILTER See Documentation/prctl/seccomp_filter.txt for details. +config HAVE_RCU_USER_QS + bool + help + Provide kernel entry/exit hooks necessary for userspace + RCU extended quiescent state. Syscalls need to be wrapped inside + rcu_user_exit()-rcu_user_enter() through the slow path using + TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs + are already protected inside rcu_irq_enter/rcu_irq_exit() but + preemption or signal handling on irq exit still need to be protected. + source "kernel/gcov/Kconfig" diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f818dd165b44..f5034f22e94b 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -191,10 +191,19 @@ extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); extern void rcu_irq_enter(void); extern void rcu_irq_exit(void); + +#ifdef CONFIG_RCU_USER_QS extern void rcu_user_enter(void); extern void rcu_user_exit(void); extern void rcu_user_enter_after_irq(void); extern void rcu_user_exit_after_irq(void); +#else +static inline void rcu_user_enter(void) { } +static inline void rcu_user_exit(void) { } +static inline void rcu_user_enter_after_irq(void) { } +static inline void rcu_user_exit_after_irq(void) { } +#endif /* CONFIG_RCU_USER_QS */ + extern void exit_rcu(void); /** diff --git a/init/Kconfig b/init/Kconfig index af6c7f8ba019..f6a1830165ce 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -441,6 +441,16 @@ config PREEMPT_RCU This option enables preemptible-RCU code that is common between the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. +config RCU_USER_QS + bool "Consider userspace as in RCU extended quiescent state" + depends on HAVE_RCU_USER_QS && SMP + help + This option sets hooks on kernel / userspace boundaries and + puts RCU in extended quiescent state when the CPU runs in + userspace. It means that when a CPU runs in userspace, it is + excluded from the global RCU state machine and thus doesn't + to keep the timer tick on for RCU. + config RCU_FANOUT int "Tree-based hierarchical RCU fanout value" range 2 64 if 64BIT diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 4138f59fa2f4..79fa2db1595b 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -400,6 +400,7 @@ void rcu_idle_enter(void) } EXPORT_SYMBOL_GPL(rcu_idle_enter); +#ifdef CONFIG_RCU_USER_QS /** * rcu_user_enter - inform RCU that we are resuming userspace. * @@ -424,7 +425,6 @@ void rcu_user_enter(void) rcu_eqs_enter(1); } - /** * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace * after the current irq returns. @@ -445,6 +445,7 @@ void rcu_user_enter_after_irq(void) rdtp->dynticks_nesting = 1; local_irq_restore(flags); } +#endif /* CONFIG_RCU_USER_QS */ /** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle @@ -548,6 +549,7 @@ void rcu_idle_exit(void) } EXPORT_SYMBOL_GPL(rcu_idle_exit); +#ifdef CONFIG_RCU_USER_QS /** * rcu_user_exit - inform RCU that we are exiting userspace. * @@ -591,6 +593,7 @@ void rcu_user_exit_after_irq(void) rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE; local_irq_restore(flags); } +#endif /* CONFIG_RCU_USER_QS */ /** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle -- 2.30.2