srcu: Introduce CLASSIC_SRCU Kconfig option
The TREE_SRCU rewrite is large and a bit on the non-simple side, so
this commit helps reduce risk by allowing the old v4.11 SRCU algorithm
to be selected using a new CLASSIC_SRCU Kconfig option that depends
on RCU_EXPERT. The default is to use the new TREE_SRCU and TINY_SRCU
algorithms, in order to help get these the testing that they need.
However, if your users do not require the update-side scalability that
is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU
to revert back to the old classic SRCU algorithm.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/init/Kconfig b/init/Kconfig
index d269f2c..558cc36 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -526,15 +526,32 @@
permits arbitrary sleeping or blocking within RCU read-side critical
sections.
+config CLASSIC_SRCU
+ bool "Use v4.11 classic SRCU implementation"
+ default n
+ depends on RCU_EXPERT && SRCU
+ help
+ This option selects the traditional well-tested classic SRCU
+ implementation from v4.11, as might be desired for enterprise
+ Linux distributions. Without this option, the shiny new
+ Tiny SRCU and Tree SRCU implementations are used instead.
+ At some point, it is hoped that Tiny SRCU and Tree SRCU
+ will accumulate enough test time and confidence to allow
+ Classic SRCU to be dropped entirely.
+
+ Say Y if you need a rock-solid SRCU.
+
+ Say N if you would like help test Tree SRCU.
+
config TINY_SRCU
bool
- default y if TINY_RCU
+ default y if TINY_RCU && !CLASSIC_SRCU
help
This option selects the single-CPU non-preemptible version of SRCU.
config TREE_SRCU
bool
- default y if !TINY_RCU
+ default y if !TINY_RCU && !CLASSIC_SRCU
help
This option selects the full-fledged version of SRCU.