rcu: Enable RCU tracepoints by default to aid in debugging
While debugging a performance issue I needed to understand why
RCU sofitrqs were firing so frequently.
Unfortunately, the RCU callback tracepoints are hidden behind
CONFIG_RCU_TRACE which defaults to off in the upstream kernel and is
likely to also be disabled in enterprise distribution configs.
Enable it by default for CONFIG_TREE_RCU. However, we must keep it
disabled for tiny RCU, because it would otherwise pull in a large
amount of code that would make tiny RCU less than tiny.
I ran some file system metadata intensive workloads (git checkout,
FS-Mark) on a variety of machines with this patch and saw no
detectable change in performance.
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b06848a..5655bd9 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1450,6 +1450,7 @@
config RCU_TRACE
bool "Enable tracing for RCU"
depends on DEBUG_KERNEL
+ default y if TREE_RCU
select TRACE_CLOCK
help
This option provides tracing in RCU which presents stats