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Date:   Tue, 24 Jan 2017 13:51:25 -0800
From:   "Paul E. McKenney" <>
Cc:,,,,,,,,,,,,,,, Matt Fleming <>,
        Mel Gorman <>,
        "Paul E. McKenney" <>
Subject: [PATCH v3 tip/core/rcu 14/18] rcu: Enable RCU tracepoints by default to aid in debugging

From: Matt Fleming <>

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 <>
Signed-off-by: Matt Fleming <>
Signed-off-by: Paul E. McKenney <>
Reviewed-by: Josh Triplett <>
 lib/Kconfig.debug | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b06848a104e6..5655bd95919a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1450,6 +1450,7 @@ 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
 	  This option provides tracing in RCU which presents stats

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