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, 10 insertions, 0 deletions

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index c64ce9c14207..61fa116efcde 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -63,3 +63,13 @@ config PREEMPT_BKL
           Say Y here if you are building a kernel for a desktop system.
           Say N if you are unsure.
 
+config RCU_TRACE
+        bool "Enable tracing for RCU - currently stats in debugfs"
+        select DEBUG_FS
+        default y
+        help
+          This option provides tracing in RCU which presents stats
+          in debugfs for debugging RCU implementation.
+
+          Say Y here if you want to enable RCU tracing
+          Say N if you are unsure.