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Commit 127781d1 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Remove TINY_PREEMPT_RCU 

TINY_PREEMPT_RCU adds significant code and complexity, but does not
offer commensurate benefits.  People currently using TINY_PREEMPT_RCU
can get much better memory footprint with TINY_RCU, or, if they really
need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively
minor degradation in memory footprint.  Please note that this move
has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545)
and on LWN (http://lwn.net/Articles/541037/

).

This commit therefore removes TINY_PREEMPT_RCU.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ]
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent efc151c3

include/linux/hardirq.h

+1 −1
Original line number Diff line number Diff line
@@ -128,7 +128,7 @@ extern void synchronize_irq(unsigned int irq); 
# define synchronize_irq(irq)	barrier()

#endif



#if defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)

#if defined(CONFIG_TINY_RCU)



static inline void rcu_nmi_enter(void)

{

include/linux/rcupdate.h

+1 −1
Original line number Diff line number Diff line
@@ -277,7 +277,7 @@ void wait_rcu_gp(call_rcu_func_t crf); 


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

#include <linux/rcutree.h>

#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)

#elif defined(CONFIG_TINY_RCU)

#include <linux/rcutiny.h>

#else

#error "Unknown RCU implementation specified to kernel configuration"

include/linux/rcutiny.h

+2 −22
Original line number Diff line number Diff line
@@ -53,16 +53,7 @@ static inline void rcu_barrier(void) 
	rcu_barrier_sched();  /* Only one CPU, so only one list of callbacks! */

}



#else /* #ifdef CONFIG_TINY_RCU */



void synchronize_rcu_expedited(void);



static inline void rcu_barrier(void)

{

	wait_rcu_gp(call_rcu);

}



#endif /* #else #ifdef CONFIG_TINY_RCU */

#endif /* #ifdef CONFIG_TINY_RCU */



static inline void synchronize_rcu_bh(void)

{
@@ -97,18 +88,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) 
	return 0;

}



#else /* #ifdef CONFIG_TINY_RCU */



void rcu_preempt_note_context_switch(void);

int rcu_preempt_needs_cpu(void);



static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

{

	*delta_jiffies = ULONG_MAX;

	return rcu_preempt_needs_cpu();

}



#endif /* #else #ifdef CONFIG_TINY_RCU */

#endif /* #ifdef CONFIG_TINY_RCU */



static inline void rcu_note_context_switch(int cpu)

{

init/Kconfig

+1 −9
Original line number Diff line number Diff line
@@ -459,18 +459,10 @@ config TINY_RCU 
	  is not required.  This option greatly reduces the

	  memory footprint of RCU.



config TINY_PREEMPT_RCU

	bool "Preemptible UP-only small-memory-footprint RCU"

	depends on PREEMPT && !SMP

	help

	  This option selects the RCU implementation that is designed

	  for real-time UP systems.  This option greatly reduces the

	  memory footprint of RCU.



endchoice



config PREEMPT_RCU

	def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )

	def_bool TREE_PREEMPT_RCU

	help

	  This option enables preemptible-RCU code that is common between

	  the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.

kernel/rcutiny_plugin.h

+0 −854

File changed.

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