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: Paul E. McKenney <[email protected]> [ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ] Reviewed-by: Josh Triplett <[email protected]>
josf · Jun 10, 2013 · 127781d · 127781d
1 parent efc151c
commit 127781d
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Showing 5 changed files with 5 additions and 887 deletions.
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
@@ -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)
 {

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
@@ -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"

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
@@ -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)
 {

diff --git a/init/Kconfig b/init/Kconfig
@@ -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.