Commit e260be67 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

Preempt-RCU: implementation 

This patch implements a new version of RCU which allows its read-side
critical sections to be preempted. It uses a set of counter pairs
to keep track of the read-side critical sections and flips them
when all tasks exit read-side critical section. The details
of this implementation can be found in this paper -

	http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf

and the article-

	http://lwn.net/Articles/253651/



This patch was developed as a part of the -rt kernel development and
meant to provide better latencies when read-side critical sections of
RCU don't disable preemption.  As a consequence of keeping track of RCU
readers, the readers have a slight overhead (optimizations in the paper).
This implementation co-exists with the "classic" RCU implementations
and can be switched to at compiler.

Also includes RCU tracing summarized in debugfs.

[ akpm@linux-foundation.org: build fixes on non-preempt architectures ]

Signed-off-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Signed-off-by: default avatarDipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
Reviewed-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e0ecfa79

fs/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -2130,4 +2130,3 @@ source "fs/nls/Kconfig" 
source "fs/dlm/Kconfig"



endmenu

include/linux/rcuclassic.h

+3 −0
Original line number Diff line number Diff line
@@ -157,5 +157,8 @@ extern void __rcu_init(void); 
extern void rcu_check_callbacks(int cpu, int user);

extern void rcu_restart_cpu(int cpu);



extern long rcu_batches_completed(void);

extern long rcu_batches_completed_bh(void);



#endif /* __KERNEL__ */

#endif /* __LINUX_RCUCLASSIC_H */

include/linux/rcupdate.h

+7 −4
Original line number Diff line number Diff line
@@ -53,7 +53,11 @@ struct rcu_head { 
	void (*func)(struct rcu_head *head);

};



#ifdef CONFIG_CLASSIC_RCU

#include <linux/rcuclassic.h>

#else /* #ifdef CONFIG_CLASSIC_RCU */

#include <linux/rcupreempt.h>

#endif /* #else #ifdef CONFIG_CLASSIC_RCU */



#define RCU_HEAD_INIT 	{ .next = NULL, .func = NULL }

#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
@@ -231,13 +235,12 @@ extern void call_rcu_bh(struct rcu_head *head, 
/* Exported common interfaces */

extern void synchronize_rcu(void);

extern void rcu_barrier(void);

extern long rcu_batches_completed(void);

extern long rcu_batches_completed_bh(void);



/* Internal to kernel */

extern void rcu_init(void);

extern void rcu_check_callbacks(int cpu, int user);



extern long rcu_batches_completed(void);

extern long rcu_batches_completed_bh(void);

extern int rcu_needs_cpu(int cpu);



#endif /* __KERNEL__ */

#endif /* __LINUX_RCUPDATE_H */

include/linux/rcupreempt.h

0 → 100644
+86 −0
Original line number Diff line number Diff line 
/*

 * Read-Copy Update mechanism for mutual exclusion (RT implementation)

 *

 * 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 (C) IBM Corporation, 2006

 *

 * Author:  Paul McKenney <paulmck@us.ibm.com>

 *

 * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>

 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.

 * Papers:

 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf

 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)

 *

 * For detailed explanation of Read-Copy Update mechanism see -

 * 		Documentation/RCU

 *

 */



#ifndef __LINUX_RCUPREEMPT_H

#define __LINUX_RCUPREEMPT_H



#ifdef __KERNEL__



#include <linux/cache.h>

#include <linux/spinlock.h>

#include <linux/threads.h>

#include <linux/percpu.h>

#include <linux/cpumask.h>

#include <linux/seqlock.h>



#define rcu_qsctr_inc(cpu)

#define rcu_bh_qsctr_inc(cpu)

#define call_rcu_bh(head, rcu) call_rcu(head, rcu)



extern void __rcu_read_lock(void);

extern void __rcu_read_unlock(void);

extern int rcu_pending(int cpu);

extern int rcu_needs_cpu(int cpu);



#define __rcu_read_lock_bh()	{ rcu_read_lock(); local_bh_disable(); }

#define __rcu_read_unlock_bh()	{ local_bh_enable(); rcu_read_unlock(); }



extern void __synchronize_sched(void);



extern void __rcu_init(void);

extern void rcu_check_callbacks(int cpu, int user);

extern void rcu_restart_cpu(int cpu);

extern long rcu_batches_completed(void);



/*

 * Return the number of RCU batches processed thus far. Useful for debug

 * and statistic. The _bh variant is identifcal to straight RCU

 */

static inline long rcu_batches_completed_bh(void)

{

	return rcu_batches_completed();

}



#ifdef CONFIG_RCU_TRACE

struct rcupreempt_trace;

extern long *rcupreempt_flipctr(int cpu);

extern long rcupreempt_data_completed(void);

extern int rcupreempt_flip_flag(int cpu);

extern int rcupreempt_mb_flag(int cpu);

extern char *rcupreempt_try_flip_state_name(void);

extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);

#endif



struct softirq_action;



#endif /* __KERNEL__ */

#endif /* __LINUX_RCUPREEMPT_H */

include/linux/rcupreempt_trace.h

0 → 100644
+99 −0
Original line number Diff line number Diff line 
/*

 * Read-Copy Update mechanism for mutual exclusion (RT implementation)

 *

 * 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 (C) IBM Corporation, 2006

 *

 * Author:  Paul McKenney <paulmck@us.ibm.com>

 *

 * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>

 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.

 * Papers:

 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf

 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)

 *

 * For detailed explanation of the Preemptible Read-Copy Update mechanism see -

 * 		 http://lwn.net/Articles/253651/

 */



#ifndef __LINUX_RCUPREEMPT_TRACE_H

#define __LINUX_RCUPREEMPT_TRACE_H



#ifdef __KERNEL__

#include <linux/types.h>

#include <linux/kernel.h>



#include <asm/atomic.h>



/*

 * PREEMPT_RCU data structures.

 */



struct rcupreempt_trace {

	long		next_length;

	long		next_add;

	long		wait_length;

	long		wait_add;

	long		done_length;

	long		done_add;

	long		done_remove;

	atomic_t	done_invoked;

	long		rcu_check_callbacks;

	atomic_t	rcu_try_flip_1;

	atomic_t	rcu_try_flip_e1;

	long		rcu_try_flip_i1;

	long		rcu_try_flip_ie1;

	long		rcu_try_flip_g1;

	long		rcu_try_flip_a1;

	long		rcu_try_flip_ae1;

	long		rcu_try_flip_a2;

	long		rcu_try_flip_z1;

	long		rcu_try_flip_ze1;

	long		rcu_try_flip_z2;

	long		rcu_try_flip_m1;

	long		rcu_try_flip_me1;

	long		rcu_try_flip_m2;

};



#ifdef CONFIG_RCU_TRACE

#define RCU_TRACE(fn, arg) 	fn(arg);

#else

#define RCU_TRACE(fn, arg)

#endif



extern void rcupreempt_trace_move2done(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_move2wait(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_e1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_i1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_ie1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_g1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_a1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_ae1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_a2(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_z1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_ze1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_z2(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_m1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_me1(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_try_flip_m2(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_check_callbacks(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_done_remove(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_invoke(struct rcupreempt_trace *trace);

extern void rcupreempt_trace_next_add(struct rcupreempt_trace *trace);



#endif /* __KERNEL__ */

#endif /* __LINUX_RCUPREEMPT_TRACE_H */

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