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 <mgor...@techsingularity.net>
Signed-off-by: Matt Fleming <m...@codeblueprint.co.uk>
---
lib/Kconfig.debug | 1 +
1 file changed, 1 insertion(+)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index a6c8db1d62f6..7fe1ff001792 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1431,6 +1431,7 @@ config RCU_CPU_STALL_TIMEOUT
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
--
2.10.0
