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 526ec1c7456a..e11bc793a91d 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