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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>
194 lines
4.1 KiB
C
194 lines
4.1 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2008
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#ifndef __LINUX_TINY_H
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#define __LINUX_TINY_H
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#include <linux/cache.h>
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void rcu_sched_qs(int cpu);
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void rcu_bh_qs(int cpu);
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#ifdef CONFIG_TINY_RCU
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#define __rcu_read_lock() preempt_disable()
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#define __rcu_read_unlock() preempt_enable()
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#else /* #ifdef CONFIG_TINY_RCU */
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void __rcu_read_lock(void);
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void __rcu_read_unlock(void);
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#endif /* #else #ifdef CONFIG_TINY_RCU */
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#define __rcu_read_lock_bh() local_bh_disable()
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#define __rcu_read_unlock_bh() local_bh_enable()
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extern void call_rcu_sched(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu));
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#define rcu_init_sched() do { } while (0)
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extern void synchronize_sched(void);
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#ifdef CONFIG_TINY_RCU
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#define call_rcu call_rcu_sched
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static inline void synchronize_rcu(void)
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{
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synchronize_sched();
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}
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static inline void synchronize_rcu_expedited(void)
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{
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synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */
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}
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static inline void rcu_barrier(void)
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{
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rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */
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}
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#else /* #ifdef CONFIG_TINY_RCU */
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void synchronize_rcu(void);
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void rcu_barrier(void);
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void synchronize_rcu_expedited(void);
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#endif /* #else #ifdef CONFIG_TINY_RCU */
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static inline void synchronize_rcu_bh(void)
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{
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synchronize_sched();
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}
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static inline void synchronize_rcu_bh_expedited(void)
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{
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synchronize_sched();
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}
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struct notifier_block;
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#ifdef CONFIG_NO_HZ
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extern void rcu_enter_nohz(void);
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extern void rcu_exit_nohz(void);
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#else /* #ifdef CONFIG_NO_HZ */
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static inline void rcu_enter_nohz(void)
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{
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}
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static inline void rcu_exit_nohz(void)
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{
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}
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#endif /* #else #ifdef CONFIG_NO_HZ */
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#ifdef CONFIG_TINY_RCU
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static inline void rcu_preempt_note_context_switch(void)
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{
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}
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static inline void exit_rcu(void)
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{
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}
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static inline int rcu_needs_cpu(int cpu)
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{
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return 0;
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}
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static inline int rcu_preempt_depth(void)
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{
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return 0;
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}
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#else /* #ifdef CONFIG_TINY_RCU */
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void rcu_preempt_note_context_switch(void);
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extern void exit_rcu(void);
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int rcu_preempt_needs_cpu(void);
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static inline int rcu_needs_cpu(int cpu)
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{
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return rcu_preempt_needs_cpu();
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}
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/*
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* Defined as macro as it is a very low level header
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* included from areas that don't even know about current
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* FIXME: combine with include/linux/rcutree.h into rcupdate.h.
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*/
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#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
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#endif /* #else #ifdef CONFIG_TINY_RCU */
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static inline void rcu_note_context_switch(int cpu)
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{
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rcu_sched_qs(cpu);
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rcu_preempt_note_context_switch();
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}
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extern void rcu_check_callbacks(int cpu, int user);
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/*
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* Return the number of grace periods.
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*/
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static inline long rcu_batches_completed(void)
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{
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return 0;
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}
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/*
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* Return the number of bottom-half grace periods.
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*/
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static inline long rcu_batches_completed_bh(void)
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{
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return 0;
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}
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static inline void rcu_force_quiescent_state(void)
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{
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}
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static inline void rcu_bh_force_quiescent_state(void)
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{
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}
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static inline void rcu_sched_force_quiescent_state(void)
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{
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}
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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extern int rcu_scheduler_active __read_mostly;
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extern void rcu_scheduler_starting(void);
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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static inline void rcu_scheduler_starting(void)
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{
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}
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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#endif /* __LINUX_RCUTINY_H */
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