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rcu: Enable RCU tracepoints by default to aid in debugging

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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>
This commit is contained in:
Matt Fleming 2016-12-23 15:17:53 +00:00 committed by Paul E. McKenney
parent fdbb9b315c
commit 961518259b
1 changed files with 1 additions and 0 deletions
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lib/Kconfig.debug
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@ -1450,6 +1450,7 @@ config RCU_CPU_STALL_TIMEOUT
config RCU_TRACE config RCU_TRACE
bool "Enable tracing for RCU" bool "Enable tracing for RCU"
depends on DEBUG_KERNEL depends on DEBUG_KERNEL
default y if TREE_RCU
select TRACE_CLOCK select TRACE_CLOCK
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This option provides tracing in RCU which presents stats This option provides tracing in RCU which presents stats