Commit f41d911f authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

rcu: Merge preemptable-RCU functionality into hierarchical RCU 



Create a kernel/rcutree_plugin.h file that contains definitions
for preemptable RCU (or, under the #else branch of the #ifdef,
empty definitions for the classic non-preemptable semantics).
These definitions fit into plugins defined in kernel/rcutree.c
for this purpose.

This variant of preemptable RCU uses a new algorithm whose
read-side expense is roughly that of classic hierarchical RCU
under CONFIG_PREEMPT. This new algorithm's update-side expense
is similar to that of classic hierarchical RCU, and, in absence
of read-side preemption or blocking, is exactly that of classic
hierarchical RCU.  Perhaps more important, this new algorithm
has a much simpler implementation, saving well over 1,000 lines
of code compared to mainline's implementation of preemptable
RCU, which will hopefully be retired in favor of this new
algorithm.

The simplifications are obtained by maintaining per-task
nesting state for running tasks, and using a simple
lock-protected algorithm to handle accounting when tasks block
within RCU read-side critical sections, making use of lessons
learned while creating numerous user-level RCU implementations
over the past 18 months.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <12509746134003-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent a157229c

include/linux/init_task.h

+15 −0
Original line number Diff line number Diff line
@@ -94,6 +94,20 @@ extern struct group_info init_groups; 
# define CAP_INIT_BSET  CAP_INIT_EFF_SET

#endif



#ifdef CONFIG_PREEMPT_RCU

#define INIT_TASK_RCU_PREEMPT(tsk)					\

	.rcu_read_lock_nesting = 0,					\

	.rcu_flipctr_idx = 0,

#elif defined(CONFIG_TREE_PREEMPT_RCU)

#define INIT_TASK_RCU_PREEMPT(tsk)					\

	.rcu_read_lock_nesting = 0,					\

	.rcu_read_unlock_special = 0,					\

	.rcu_blocked_cpu = -1,						\

	.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry),

#else

#define INIT_TASK_RCU_PREEMPT(tsk)

#endif



extern struct cred init_cred;



#ifdef CONFIG_PERF_COUNTERS
@@ -173,6 +187,7 @@ extern struct cred init_cred; 
	INIT_LOCKDEP							\

	INIT_FTRACE_GRAPH						\

	INIT_TRACE_RECURSION						\

	INIT_TASK_RCU_PREEMPT(tsk)					\

}

include/linux/rcupdate.h

+1 −1
Original line number Diff line number Diff line
@@ -66,7 +66,7 @@ extern void rcu_scheduler_starting(void); 
extern int rcu_needs_cpu(int cpu);

extern int rcu_scheduler_active;



#if defined(CONFIG_TREE_RCU)

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)

#include <linux/rcutree.h>

#elif defined(CONFIG_PREEMPT_RCU)

#include <linux/rcupreempt.h>

include/linux/rcupreempt.h

+4 −0
Original line number Diff line number Diff line
@@ -98,6 +98,10 @@ static inline long rcu_batches_completed_bh(void) 
	return rcu_batches_completed();

}



static inline void exit_rcu(void)

{

}



#ifdef CONFIG_RCU_TRACE

struct rcupreempt_trace;

extern long *rcupreempt_flipctr(int cpu);

include/linux/rcutree.h

+16 −0
Original line number Diff line number Diff line
@@ -35,14 +35,30 @@ extern void rcu_bh_qs(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 exit_rcu(void);



#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */



static inline void __rcu_read_lock(void)

{

	preempt_disable();

}



static inline void __rcu_read_unlock(void)

{

	preempt_enable();

}



static inline void exit_rcu(void)

{

}



#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */



static inline void __rcu_read_lock_bh(void)

{

	local_bh_disable();

include/linux/sched.h

+37 −0
Original line number Diff line number Diff line
@@ -1210,6 +1210,13 @@ struct task_struct { 
	int rcu_flipctr_idx;

#endif /* #ifdef CONFIG_PREEMPT_RCU */



#ifdef CONFIG_TREE_PREEMPT_RCU

	int rcu_read_lock_nesting;

	char rcu_read_unlock_special;

	int rcu_blocked_cpu;

	struct list_head rcu_node_entry;

#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */



#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)

	struct sched_info sched_info;

#endif
@@ -1723,6 +1730,36 @@ extern cputime_t task_gtime(struct task_struct *p); 
#define tsk_used_math(p) ((p)->flags & PF_USED_MATH)

#define used_math() tsk_used_math(current)



#ifdef CONFIG_TREE_PREEMPT_RCU



#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */

#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */

#define RCU_READ_UNLOCK_GOT_QS  (1 << 2) /* CPU has responded to RCU core. */



static inline void rcu_copy_process(struct task_struct *p)

{

	p->rcu_read_lock_nesting = 0;

	p->rcu_read_unlock_special = 0;

	p->rcu_blocked_cpu = -1;

	INIT_LIST_HEAD(&p->rcu_node_entry);

}



#elif defined(CONFIG_PREEMPT_RCU)



static inline void rcu_copy_process(struct task_struct *p)

{

	p->rcu_read_lock_nesting = 0;

	p->rcu_flipctr_idx = 0;

}



#else



static inline void rcu_copy_process(struct task_struct *p)

{

}



#endif



#ifdef CONFIG_SMP

extern int set_cpus_allowed_ptr(struct task_struct *p,

				const struct cpumask *new_mask);

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