rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status

Because the adaptive synchronize_srcu_expedited() approach has
worked very well in testing, remove the kernel parameter and
replace it by a C-preprocessor macro.  If someone finds problems
with this approach, a more complex and aggressively adaptive
approach might be required.

Longer term, SRCU will be merged with the other RCU implementations,
at which point synchronize_srcu_expedited() will be event driven,
just as synchronize_sched_expedited() currently is.  At that point,
there will be no need for this adaptive approach.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 0 insertions, 15 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 526ec1c..e11bc79 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -497,21 +497,6 @@ config RCU_BOOST_DELAY
 
 	  Accept the default if unsure.
 
-config SRCU_SYNCHRONIZE_DELAY
-	int "Microseconds to delay before waiting for readers"
-	range 0 20
-	default 10
-	help
-	  This option controls how long SRCU delays before entering its
-	  loop waiting on SRCU readers.  The purpose of this loop is
-	  to avoid the unconditional context-switch penalty that would
-	  otherwise be incurred if there was an active SRCU reader,
-	  in a manner similar to adaptive locking schemes.  This should
-	  be set to be a bit longer than the common-case SRCU read-side
-	  critical-section overhead.
-
-	  Accept the default if unsure.
-
 endmenu # "RCU Subsystem"
 
 config IKCONFIG