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: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 4 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 12aa13e13150..d32c14de270e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -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 */