Commit 2b1d5024 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 9a0c6fef

arch/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -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"

include/linux/rcupdate.h

+9 −0
Original line number Diff line number Diff line
@@ -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);



/**

init/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcutree.c

+4 −1
Original line number Diff line number Diff line
@@ -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

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