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| Started by | Matt Fleming <matt@codeblueprint.co.uk> |
|---|---|
| First post | 2016-12-23 16:20 +0100 |
| Last post | 2016-12-23 18:20 +0100 |
| Articles | 2 — 2 participants |
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[PATCH] rcu: Enable RCU tracepoints by default to aid in debugging Matt Fleming <matt@codeblueprint.co.uk> - 2016-12-23 16:20 +0100
Re: [PATCH] rcu: Enable RCU tracepoints by default to aid in debugging "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-12-23 18:20 +0100
| From | Matt Fleming <matt@codeblueprint.co.uk> |
|---|---|
| Date | 2016-12-23 16:20 +0100 |
| Subject | [PATCH] rcu: Enable RCU tracepoints by default to aid in debugging |
| Message-ID | <sRzNw-6F-11@gated-at.bofh.it> |
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> --- 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
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| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Date | 2016-12-23 18:20 +0100 |
| Subject | Re: [PATCH] rcu: Enable RCU tracepoints by default to aid in debugging |
| Message-ID | <sRBFD-1lR-13@gated-at.bofh.it> |
| In reply to | #1546890 |
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 <mgorman@techsingularity.net> > Signed-off-by: Matt Fleming <matt@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 >
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