[PATCH] Kconfig.debug: Set DEBUG_MUTEX to off by default

[PATCH] Kconfig.debug: Set DEBUG_MUTEX to off by default

[Tim Chen]

Hi,

DEBUG_MUTEX flag is on by default in current kernel configuration.
 
During performance testing, we saw mutex debug functions like
mutex_debug_check_no_locks_freed (called by kfree()) is expensive as it
goes through a global list of memory areas with mutex lock and do the
checking.  For benchmarks such as Volanomark and Hackbench, we have seen
more than 40% drop in performance on some platforms.  We suggest to set
DEBUG_MUTEX off by default.  Or at least do that later when we feel that
the mutex changes in the current code have stabilized.

Tim Chen

Signed-off-by: Tim Chen <tim.c.chen@intel.com>

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -101,7 +101,7 @@ config DEBUG_PREEMPT
 
 config DEBUG_MUTEXES
 	bool "Mutex debugging, deadlock detection"
-	default y
+	default n
 	depends on DEBUG_KERNEL
 	help
 	 This allows mutex semantics violations and mutex related deadlocks

Re: [PATCH] Kconfig.debug: Set DEBUG_MUTEX to off by default

[Arjan van de Ven]

On Fri, 2006-04-07 at 09:56 -0700, Tim Chen wrote:
> Hi,
> 
> DEBUG_MUTEX flag is on by default in current kernel configuration.
>  
> During performance testing, we saw mutex debug functions like
> mutex_debug_check_no_locks_freed (called by kfree()) is expensive as it
> goes through a global list of memory areas with mutex lock and do the
> checking.  For benchmarks such as Volanomark and Hackbench, we have seen
> more than 40% drop in performance on some platforms.  We suggest to set
> DEBUG_MUTEX off by default.  Or at least do that later when we feel that
> the mutex changes in the current code have stabilized.
> 
> Tim Chen
> 
> Signed-off-by: Tim Chen <tim.c.chen@intel.com>
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -101,7 +101,7 @@ config DEBUG_PREEMPT
>  
>  config DEBUG_MUTEXES
>  	bool "Mutex debugging, deadlock detection"
> -	default y
> +	default n

don't do default n, just remove the line instead ;)