a57eb940d1
Implement a small-memory-footprint uniprocessor-only implementation of preemptible RCU. This implementation uses but a single blocked-tasks list rather than the combinatorial number used per leaf rcu_node by TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies processing. This version also takes advantage of uniprocessor execution to accelerate grace periods in the case where there are no readers. The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU. This implementation is a step towards having RCU implementation driven off of the SMP and PREEMPT kernel configuration variables, which can happen once this implementation has accumulated sufficient experience. Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as suggested by Steve Rostedt in order to avoid the compiler-reordering issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183). As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte savings compared to CONFIG_TREE_PREEMPT_RCU. Of course, for non-real-time workloads, CONFIG_TINY_RCU is even better. CONFIG_TREE_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 6170 825 28 7023 kernel/rcutree.o ---- 7026 Total CONFIG_TINY_PREEMPT_RCU text data bss dec filename 13 0 0 13 kernel/rcupdate.o 2081 81 8 2170 kernel/rcutiny.o ---- 2183 Total CONFIG_TINY_RCU (non-preemptible) text data bss dec filename 13 0 0 13 kernel/rcupdate.o 719 25 0 744 kernel/rcutiny.o --- 757 Total Requested-by: Loïc Minier <loic.minier@canonical.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
131 lines
3.3 KiB
C
131 lines
3.3 KiB
C
/*
|
|
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
|
|
*
|
|
* Copyright IBM Corporation, 2008
|
|
*
|
|
* Author: Dipankar Sarma <dipankar@in.ibm.com>
|
|
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical algorithm
|
|
*
|
|
* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
|
|
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
|
|
*
|
|
* For detailed explanation of Read-Copy Update mechanism see -
|
|
* Documentation/RCU
|
|
*/
|
|
|
|
#ifndef __LINUX_RCUTREE_H
|
|
#define __LINUX_RCUTREE_H
|
|
|
|
struct notifier_block;
|
|
|
|
extern void rcu_sched_qs(int cpu);
|
|
extern void rcu_bh_qs(int cpu);
|
|
extern void rcu_note_context_switch(int cpu);
|
|
extern int rcu_needs_cpu(int cpu);
|
|
|
|
#ifdef CONFIG_TREE_PREEMPT_RCU
|
|
|
|
extern void __rcu_read_lock(void);
|
|
extern void __rcu_read_unlock(void);
|
|
extern void synchronize_rcu(void);
|
|
extern void exit_rcu(void);
|
|
|
|
/*
|
|
* Defined as macro as it is a very low level header
|
|
* included from areas that don't even know about current
|
|
*/
|
|
#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
|
|
|
|
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static inline void __rcu_read_lock(void)
|
|
{
|
|
preempt_disable();
|
|
}
|
|
|
|
static inline void __rcu_read_unlock(void)
|
|
{
|
|
preempt_enable();
|
|
}
|
|
|
|
#define synchronize_rcu synchronize_sched
|
|
|
|
static inline void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
static inline int rcu_preempt_depth(void)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static inline void __rcu_read_lock_bh(void)
|
|
{
|
|
local_bh_disable();
|
|
}
|
|
static inline void __rcu_read_unlock_bh(void)
|
|
{
|
|
local_bh_enable();
|
|
}
|
|
|
|
extern void call_rcu_sched(struct rcu_head *head,
|
|
void (*func)(struct rcu_head *rcu));
|
|
extern void synchronize_rcu_bh(void);
|
|
extern void synchronize_sched(void);
|
|
extern void synchronize_rcu_expedited(void);
|
|
|
|
static inline void synchronize_rcu_bh_expedited(void)
|
|
{
|
|
synchronize_sched_expedited();
|
|
}
|
|
|
|
extern void rcu_barrier(void);
|
|
|
|
extern void rcu_check_callbacks(int cpu, int user);
|
|
|
|
extern long rcu_batches_completed(void);
|
|
extern long rcu_batches_completed_bh(void);
|
|
extern long rcu_batches_completed_sched(void);
|
|
extern void rcu_force_quiescent_state(void);
|
|
extern void rcu_bh_force_quiescent_state(void);
|
|
extern void rcu_sched_force_quiescent_state(void);
|
|
|
|
#ifdef CONFIG_NO_HZ
|
|
void rcu_enter_nohz(void);
|
|
void rcu_exit_nohz(void);
|
|
#else /* CONFIG_NO_HZ */
|
|
static inline void rcu_enter_nohz(void)
|
|
{
|
|
}
|
|
static inline void rcu_exit_nohz(void)
|
|
{
|
|
}
|
|
#endif /* CONFIG_NO_HZ */
|
|
|
|
/* A context switch is a grace period for RCU-sched and RCU-bh. */
|
|
static inline int rcu_blocking_is_gp(void)
|
|
{
|
|
return num_online_cpus() == 1;
|
|
}
|
|
|
|
extern void rcu_scheduler_starting(void);
|
|
extern int rcu_scheduler_active __read_mostly;
|
|
|
|
#endif /* __LINUX_RCUTREE_H */
|