On Fri, Dec 23, 2016 at 03:17:53PM +0000, Matt Fleming wrote:
> 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>
Queued for testing and review, thank you!
Thanx, Paul
> ---
> 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
>
